Yeah, I had this problem, not with a server, just my client.
Whenever I tried to devmap my maps, I was getting a BotFreeClient error.
It applied to all maps I tried to run, I could join any servers no prob, it just had a problem with me running the map from my own client.
Strangely enough, I found a weirdly named .pk3 in my user Base folder.
It had a .qvm in it. I removed the .pk3 and bingo no more problem.
(I prolly d/l'd it when joining a server.)
This prolly wont fix this error for a server, but if it's only your client havin the problem, have a l00k in your base folders for any extra .qvm's that shouldn't be there.