Garry's Mod is not starting due to an error

Ok, so I open my Steam to play a bit of Garry’s Mod and I notice Garry’s Mod does not want to open, so I go the library and I see that it is updating. After it is done updating I open it up and I am greeted with the following error:

I am not sure if this is something I have caused but I am not sure what I need to due in order to solve it,
Thanks.

Edit:
Also I have checked my processes and hl2.exe is not open.

Edit 2:
Just kept clicking Garry’s Mod in the library and then it worked.

Mine does this daily, I just restart steam and it works fine

i now cannot launch gmod at all everytime it does this even after restarts

I just kept trying to open Garry’s Mod and restarting Steam and it work after some time