First I'd like to say thank You, because this plugin saved me a lot of work, unfortunately parts of it are not working any more. A few days ago tweets stopped to become posts as well. Maybe it 's because I switched from 3.0.x to 3.0.4? The Bit.ly option is also not working, but I don 't know if that has worked before. I never used that before, but I wanted to try it now : )
Sending the tweets to Twitter works as usual, so it seems to be a WordPress problem.