[gm13] Single player map invalid??

keep getting the pop up below when i start single player. tryed to select a diffrent map and still getting the same thing

Did you try validating the game cache? Defragmenting? Reinstalling?

Does GMod work on Multiplayer?
Did you try the default maps (construct, flatgrass, etc.)?

Are the maps custom? Make sure they’re compiled correctly

Multiplier works,
Tried all default maps and tried custom ones
Tried everything that you have said and still getting the same error