For the last couple of days I noticed that my BB won't delete messages in SMS inbox and some messages started to duplicate in inbox. When I want to delete the message nothing happens (message still remains in inbox but when I open it there's a blank field). I don't know what could be the problem. I updated it 2 months ago and it worked like a charm so far...

Have you tried popping the battery out for a few seconds and then putting it back in? That cures a lot of similar problems.

Just did that. Works perfectly now. Didn't think that could be the solution Thanks a lot!