I don't think it's mod. I have same problem and do not have any BlackSmith mod...
EDIT: I found the problem. It's ShowDurabilty 2 mod... I will test it... YUP! This is the crash-causer. The topic is to close now...
For you I'll try to contact to Show Durabilty 2 mod creator and talk about it.
EDIT2: I solved it!
Go to ShowDurability2.jar file in mods and find BlackSmith in /com/nemock. Then DELETE it.