What Lemon said to do is basically re-installing G-Mod but without waiting 5 minutes (depending on download speed, could be like 2 days for ERROR...) Re-name your garrysmod/garrysmod folder to something else and run g-mod again on ZS. Everything will re-download but it should work. Once it works, you can copy over folder by folder until it stops working again then you can see what the problem was.