# Launching Session Error After Building HLODs

**URL:** <https://forums.unrealengine.com/t/launching-session-error-after-building-hlods/1545996>\
**Category:** Issues and Bug Reporting\
**Tags:** error, sessions, unreal-editor-for-fortnite, fortnite\
**Created:** [December 22, 2023, 4:56pm UTC](https://forums.unrealengine.com/t/launching-session-error-after-building-hlods/1545996 "2023-12-22T16:56:08Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ShalevFNC](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/shalevfnc/32/1113451_2.png) [@ShalevFNC](https://forums.unrealengine.com/u/ShalevFNC)\
**Post date:** [December 22, 2023, 4:56pm UTC](https://forums.unrealengine.com/t/launching-session-error-after-building-hlods/1545996/1 "2023-12-22T16:56:08Z")

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Hello, today I built HLODs in my UEFN project. I’m trying to launch a session after building HLODs and I get the error that you can see in the image, I’ll add the error to this message as well:

We encountered an error preparing your project. Error: errors.com.epicgames.content-service.cook-failure, An error occurred while communicating with the game servers (Content (re)cook error errors.com.epicgames.cookplugin.cookfailure.  
JOB\_ID=c30f5576-9957-4373-807e-35327cbb2149)., CookJobId:c30f5576-9957-4373-807e-35327cbb2149  
LogWindows: Error: appError called: Assertion failed: Owner-\>IsMeshDescriptionValid(0) [File:D:\build++Fortnite\Sync\Engine\Source\Runtime\Engine\Private\StaticMesh.cpp] [Line: 3088]  
Bad MeshDescription on /fd621f1c-4653-4621-f449-dcb9e992ad1b/ **externalactors** /finallyarcaneroyalechapter3/0/0h/0k2k51hkj0s2195eqz0uhl.StaticMesh\_ArcaneRoyale\_HLODLayer\_0

LogThreadingWindows: Error: Runnable thread Background Worker #23 crashed.  
LogWindows: Error: appError called: Assertion failed: Owner-\>IsMeshDescriptionValid(0) [File:D:\build++Fortnite\Sync\Engine\Source\Runtime\Engine\Private\StaticMesh.cpp] [Line: 3088]  
Bad MeshDescription on /fd621f1c-4653-4621-f449-dcb9e992ad1b/ **externalactors** /finallyarcaneroyalechapter3/0/0h/0k2k51hkj0s2195eqz0uhl.StaticMesh\_ArcaneRoyale\_HLODLayer\_0

LogThreadingWindows: Error: Runnable thread Background Worker #23 crashed.

 ![errorimage](https://d3kjluh73b9h9o.cloudfront.net/original/4X/4/0/d/40d7ed6f3d91fdda41ff3bd9ce5edf41e1662a96.png)

This is the error, I tried to untick all the custom static meshes that I imported with the options “Include Actor in HLOD” and “Include Component in HLOD” and I unticked these options for all the custom static meshes that imported.

I tried to launch session from PC and I got this error, tried to connect to platfrom and entering the island from Phone and I still get the error also when trying to launch session in Phone device.

Please help me fix it, this project is important for me and I have to find a fix for it as soon as possible. Thank you and have a good day.

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**Author:** ![Bug-Reporter](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/bug-reporter/32/997076_2.png) [@Bug-Reporter](https://forums.unrealengine.com/u/Bug-Reporter)\
**Post date:** [December 22, 2023, 5:01pm UTC](https://forums.unrealengine.com/t/launching-session-error-after-building-hlods/1545996/2 "2023-12-22T17:01:50Z")

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The status of UCB-1138 incident has been moved from ‘Awaiting Validation’ to ‘Closed’. Resolution Reason: ‘Duplicate’

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**Author:** ![Alien-lady](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Alien-lady](https://forums.unrealengine.com/u/Alien-lady)\
**Post date:** [December 23, 2023, 12:45am UTC](https://forums.unrealengine.com/t/launching-session-error-after-building-hlods/1545996/3 "2023-12-23T00:45:34Z")

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> Thank you for your report! Can you please re-post using the “New Issue” option on the [Issues and Bug Reporting forums](https://forums.unrealengine.com/tags/c/general/issues-and-bug-reporting/172/fortnite)? Posts with this feature are connected directly into our development team so we can quickly get to them!  
> For more information, such as how to get the reference ID, please check out the article here: [Using the Creative and UEFN Bug Reporting Form](https://create.fortnite.com/news/using-the-creative-and-uefn-bug-reporting-form)