|i know how to fix the hl2.exe error on steam source engine game on vista system|
1. Right click on your game in steam
2. Click "properties"
3. Click "set launch options"
4. enter the cmd "-dxlevel 81" (without ")
5. click "ok" and close properties
6. launch the game
7. if the game is not working properly try the cmd "-dxlevel 70"
setting the direct x level worked for me
the fix can be found under steam troubleshooter under game crashes section allthough steam also tell you to type the cmds
and +mat_forcehardwaresync 0
and these can also fix some games problems
but it seems direct x is the only thing you need to change on gmod10
this is a link to the support page containing this fix
scroll to Set Game Launch Options and Disable Problematic Hardware