Half-Life 2 -- Garry's Mod Crash Question

Whenever I try to start Garry’s Mod for Half-Life 2 by running GMod10[Final].exe, I get the following error message:

the instruction at “0x0f633e2c” referenced memory at “0x0d5ca1a0”. The memory could not be “read”. Click on OK to terminate the program

Accompanied by a crash to the desktop. Anyone know a way to fix this? For reference, I’ve got the following installed:

DoD GMod
MegaPack GMod
GMod 10

I’d really like this effing thing to work :mad: