Time machine Cannot complete Backup

I recently re-installed Lion and deleted everything from my Time capsule
I Set it up New and Time machine started Backups
Those were really small and they seem to increase while backing up but Finally i get the error Message that Time machine Cannot complete the Backup does Anyone have an Idea?
Thanks in advance!

If it did not give you an error I suspect it lost connection.

does the backup has to run through completely one time? because - i set it up, then let it backup, then grab my laptop go down for work and it loses connection. later, when i´m back, it backs up again. can this cause the problem?
thanks

In Lion the Time Machine backup will start even if your external hard drive is not attached. What it will do is create a hidden image of the backup on your MBP hard drive and copy it to the external drive when it's attached again. If you don't want that to happen, you must turn off Time Machine when disconnecting the external hard drive.