Thank you for that information. I’ve never seen this error message before unfortunately and actually can’t seem to find much about it. The little bit that I did find seemed to be caused by firewalls or virus-protection software. Could you try disabling any of these types of software you have on your computer temporarily to see if they are conflicting with the IDE? Also, be sure that everything related to UE4 and VS is being run as administrator.
If neither of those help, just so that we can narrow it down a bit more, can you try building a basic code project outside of UE4, such as a Hello World program in 2015? This’ll let us know that the problem is between VS and the Engine instead of just a problem with VS itself or installed SDKs.
I should’ve asked this previously but have you used any previous versions of the engine where you didn’t have any issues? Are these issues new to 4.11 for you?