An error occurred while updating Garry's Mod (disk write error)

Every time I try to launch Garry’s Mod I get this error


An error occurred while updating Garry's Mod (disk write error).

I can open other Source games just fine, but I can’t start GMod. I’ve tried most things, such as verifying game cache and running as administrator but nothing seems to fix it. Anybody got any ideas?

Try renaming your Garry’s Mod folder to garrysmod_old and reinstalling.