How To Fix Content Mounting In Garry's Mod.

[Kigen]

To fix the mounting issues. You must mount your games and verify it's cache.

Games you need to verify:

 

CS:S

HL2

HL2:EP1

HL2:EP2

TF2

 

To Verify it you must: Right click on the game in steam, than click 'properties.' Click on the last tab called "Betas" than click on the tab and select: Beta- SteamPipe beta. Finally close the properties tab and run the game, it should update it. Once complete play Garry's Mod (make sure the games are mounted into GMOD. to check click the 'game controller on the bottom right of the screen) and join the server, the errors should be gone.

 

http://facepunch.com/showthread.php?t=1271741