After an upgrade to 3.4, Winbox reports that it "Could not save configuration"
There is a thread that reports this error also
http://forum.mikrotik.com/viewtopic.php?f=1&t=93307
and I've tried deleting the contents in
C:\Users\xxxxxxx\AppData\Roaming\Mikrotik\Winbox
but that didn't help. Anything else I can try?