"Your version of (insert map name here) differs

[LKC6]

I know what to do fix it, but I can't find the map location in the Workshop. Can someone help?

 

[valerstein]

Just remove the map from your garry's mod directory and rejoin the server. It should fix it.

 

[Forks]

You can also search the map name on steam workshop, I think it was rp_salvation_redux, and just subscribe to that. Worked for me.

 

[Gangleider]

this should no longer be a problem as of the latest gmod update