I have been trying to install UE4 on my desktop for awhile now and I keep getting this same error. I have tried emptying my temp folder and uninstalling/reinstalling even the launcher but I still get this error when i try to install the engine. It usually begins the installation and gets to about 28% before I get the error message. This happens with any version of the engine which is why I thought it might a launcher issue to begin with.
Hi Evil_Gizmo,
I’m sorry that you are having an issue with the Epic Games Launcher. In order for us to offer the best support, we have recently modified the process for how Epic Games can help troubleshoot your Launcher issue. Please visit http://help.epicgames.com/ for Launcher technical support Here you can find information and solutions for common issues, as well as a contact form if you still need additional assistance. To access the contact form, please use the “Email Us” button under the “Contact Us” section. Thanks!
In addition, this article from the support center may be helpful since it deals with a similar issue.