Problems occured running accepting change sets

Hi!

We are a Team of 7 Students and are running our own Jazz- Server and are developing using Eclipse RCP.
It was working fine for me since we startet in April 2012. Threee days ago, i changed my flow target to get only the changes of another student and test them. even this worked fine. After testing, i switched back to the main flow of our project and discarded the changes of my partner.

But now i am not able to get any changes on the main flow. i am getting the error in the screenshot. Any ideas?

Thanks

http://www.bilder-space.de/show_img.php?img=8c1ee9-1338532534.jpg&size=original

update:
i am able to check in and deliver new change sets for existing plugins we developed. but i am getting an error when i want to check in new plugins (see new screenshot). The error described above is still existing.

http://www.bilder-space.de/show_img.php?img=c00c9b-1338532824.jpg&size=original