Garry's Mod Update not installing properly

For some reason, ever since the update which came out yesterday, my Garry’s Mod refuses to update properly.

I have tried searching the Hard Disk that the games installed in for errors but apparently there are no errors when it finishes searching. I’ve also tried verifying the game cache but it comes up with the same error.

This is the error that pops up when i try to install it:

As the error suggests, Steam cannot write that file onto your disk.

Either try running Steam as administrator, move your GMod installation and check if you even have enough storage on drive D.

That’s all I can tell you. It’s not a problem with the game.