# Lightmass crashed: Assertion failed and more **URL:** \ **Category:** Rendering\ **Tags:** Lightmass, assertion-failed, unreal-engine, crash, question\ **Created:** [January 16, 2018, 1:40am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662 "2018-01-16T01:40:08Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MinhMX](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@MinhMX](https://forums.unrealengine.com/u/MinhMX)\ **Post date:** [January 16, 2018, 1:40am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/1 "2018-01-16T01:40:08Z")
Hi guys, I got a problem. When I clicked Build, after a short time, the Message Log appeared with the error: Lightmass crashed: Assertion failed … and so many things below. Please see the image below. So hope you guys can help me solve this problem. Many thanks and have a good day!!! ![227168-capture1.jpg](https://d3kjluh73b9h9o.cloudfront.net/original/4X/e/0/3/e03cf70d6ba93e6ac1b6c5975ea060b57544d9ec.jpeg) ---
**Author:** ![Ihab\_Kalache](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Ihab\_Kalache](https://forums.unrealengine.com/u/Ihab_Kalache)\ **Post date:** [January 17, 2018, 8:13pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/2 "2018-01-17T20:13:24Z")
I installed the 4.19 preview and tried building the light maps and package the project into an exe and it worked. I think something happened to my 4.18 or it could be datasmith bug… ---
**Author:** ![Rseriki\_HOK](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Rseriki\_HOK](https://forums.unrealengine.com/u/Rseriki_HOK)\ **Post date:** [January 23, 2018, 5:36pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/3 "2018-01-23T17:36:22Z")
I had the same problem with 4.18. I was able to solve it by opening the Swarm agent window, validate the cache and then clearing the cache. ![228157-swarm-window.jpg](https://d3kjluh73b9h9o.cloudfront.net/original/4X/a/6/1/a61ff2ab39d49b64e5bd10625b531cb4eac9fa30.jpeg) ---
**Author:** ![Rosium](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Rosium](https://forums.unrealengine.com/u/Rosium)\ **Post date:** [August 2, 2018, 10:23pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/4 "2018-08-02T22:23:27Z")
How do you open the swarm agent application?? It never opens when i click on the exe. but it shows up on the task manager ---
**Author:** ![13oscarmartr2018](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@13oscarmartr2018](https://forums.unrealengine.com/u/13oscarmartr2018)\ **Post date:** [October 21, 2018, 7:54pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/5 "2018-10-21T19:54:03Z")
Awesome way to fix that, thanks for sharing that knowledge! ---
**Author:** ![anonymous\_user\_8c32e2fe1](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@anonymous\_user\_8c32e2fe1](https://forums.unrealengine.com/u/anonymous_user_8c32e2fe1)\ **Post date:** [November 9, 2018, 12:14am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/6 "2018-11-09T00:14:27Z")
![258940-capturar.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/1/1/4/11457ad6d4493e92fece6154740d3a0a7cc1c384.png) When you are building your light, the Swarm Agent Icon shows in the windows icon bar ---
**Author:** ![anonymous\_user\_5b0b8904](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@anonymous\_user\_5b0b8904](https://forums.unrealengine.com/u/anonymous_user_5b0b8904)\ **Post date:** [December 3, 2018, 8:10pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/7 "2018-12-03T20:10:41Z")
Thank you so much worked for me. That was killing me ---
**Author:** ![lenouschka](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@lenouschka](https://forums.unrealengine.com/u/lenouschka)\ **Post date:** [December 5, 2018, 5:12pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/8 "2018-12-05T17:12:28Z")
worked for me too, many thanks!! \<3 ---
**Author:** ![Djoletta](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Djoletta](https://forums.unrealengine.com/u/Djoletta)\ **Post date:** [December 27, 2018, 4:52pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/9 "2018-12-27T16:52:42Z")
Thank you, worked for me also!!! ---
**Author:** ![Cobbra3d](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Cobbra3d](https://forums.unrealengine.com/u/Cobbra3d)\ **Post date:** [January 2, 2019, 8:23pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/10 "2019-01-02T20:23:09Z")
thank you thank you thank you so much ---
**Author:** ![AksAman](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@AksAman](https://forums.unrealengine.com/u/AksAman)\ **Post date:** [May 30, 2019, 9:10pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/11 "2019-05-30T21:10:15Z")
Thanks for the swarm application fix!! It worked. ---
**Author:** ![Imagine-Games](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Imagine-Games](https://forums.unrealengine.com/u/Imagine-Games)\ **Post date:** [October 10, 2019, 5:58pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/12 "2019-10-10T17:58:10Z")
worked for me, thanks! ---
**Author:** ![NINJAROCK66](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@NINJAROCK66](https://forums.unrealengine.com/u/NINJAROCK66)\ **Post date:** [October 15, 2019, 1:14pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/13 "2019-10-15T13:14:08Z")
funciono gracias: Rseriki\_HOK ---
**Author:** ![Federico\_Vignone](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Federico\_Vignone](https://forums.unrealengine.com/u/Federico_Vignone)\ **Post date:** [June 28, 2020, 2:48am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/14 "2020-06-28T02:48:14Z")
Hello guys! I have a similar problem, but it is not solved with the Swarm Agent! What can be? Thank you! ![305614-sin-titulo.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/a/f/2/af2cbcf1c0f3457ca9c47d601af93f2e23073695.png) ---
**Author:** ![abuahmed](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@abuahmed](https://forums.unrealengine.com/u/abuahmed)\ **Post date:** [July 22, 2020, 7:08am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/15 "2020-07-22T07:08:15Z")
I doesn’t work for me and still crashing after validate/cleaning the cache, any idea what should I try next? Thank you. ---
**Author:** ![abuahmed](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@abuahmed](https://forums.unrealengine.com/u/abuahmed)\ **Post date:** [July 22, 2020, 7:08am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/16 "2020-07-22T07:08:41Z")
It doesn’t work for me and it’s still crashing after validate/cleaning the cache, any idea what should I try next? Thank you. ---
**Author:** ![PDubulous](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/pdubulous/32/1194655_2.png) [@PDubulous](https://forums.unrealengine.com/u/PDubulous)\ **Post date:** [July 28, 2020, 1:56pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/17 "2020-07-28T13:56:54Z")
You sir, are a hero today. ---
**Author:** ![Rflaae](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Rflaae](https://forums.unrealengine.com/u/Rflaae)\ **Post date:** [September 16, 2020, 8:53pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/18 "2020-09-16T20:53:49Z")
Thanks! 😉 ---
**Author:** ![ChaoticMuki](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@ChaoticMuki](https://forums.unrealengine.com/u/ChaoticMuki)\ **Post date:** [November 23, 2020, 12:27pm UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/19 "2020-11-23T12:27:07Z")
worked for me too, thanks 🙂 ---
**Author:** ![Jeremy\_RosBroz](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Jeremy\_RosBroz](https://forums.unrealengine.com/u/Jeremy_RosBroz)\ **Post date:** [July 28, 2021, 1:26am UTC](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662/20 "2021-07-28T01:26:14Z")
Worked for me Thank you. UE 4.26 [Next page](https://forums.unrealengine.com/t/lightmass-crashed-assertion-failed-and-more/414662.md?page=2)