Hi.
I to got some serious trouble with version 4.12.6 (pro) , not same as you, but serious enough. The solution was quite simple, un-install version 4.12.6...
Now I use my previous version 4.10.0 (pro), and everything is back to normal again..

Hoped it was to some help..
U can take a look on this thread as well, we are not the only with 4.12.6 trouble!

http://www.gnutellaforums.com/showthread.php?t=61085

Sincerly Seven.