Garry's Mod won't run

[BeaverMon]

I have installed Garry's Mod 8 v3, opened it, and this popup comes up;

Engine Error
MountFilesystem ( 242 ) failed: SteamMountFilesystem(3044,242,0x46dfbfc=,0x46dfd0c) failed with error 114: Cache needs decryption

I hit OK, and this comes up;

Garry's Mod Eight v3b: hl2.exe - Application Error
The instruction at "0x0127cc80" referenced memory at "0x0127cc80". The memory could not be "read".

Click on OK to terminate the program

Please help. :(

EDIT: Having to run CS: S got Garry's Mod to work. I LOVE this new Gravity Gun! :D I've been tossing ragdolls around with it, it was hullarious. :) True Zero-Point Energy. ;)
I spawned a Strider, and the damn thing fell right infront of me. Dead. Was like "WOAH!!!". :eek:

[frohman2]

I can't get GMOD 10 to work after CHKDSK ran in windows vista Don't know why butif anyone has this problem please reply.
I also have a problem removing GMOD 9,8 and 7