To be honest, I never explicitly banned it.
The default configuration of the Tinyboard software is to add tor exit nodes to its DNS blacklist. I don't use tor myself, nor have I been approached about it until now, so I guess I haven't given it thought.
I've gone ahead and updated the blacklist to allow tor nodes, can you go ahead and try it now and tell me how it works? I'll help troubleshoot what I can.