Gmod 13 crashes on change level with an engine error

[RaptorRed]

Was about to play with my friend some garrysmod but when he tried to change the level he crashed with "Engine error closing pack file with open files"
as he stated, what could be the cause of this error, and how can he fix it?

I can't give much details about the crash because I wasn't the one experiencing it.

[Rigstig]

got the same thing

[Zimtower]

We are having issues too with changelevel, it makes all of our entities disappear and IsValid gets called with a result of nil. We are using a clean updated server running TTT on Windows btw.