Hope there are some svn wizards here.
Somehow one of my files dropped out of svn i.e. it got a ? to its icon.
Confused as i was i added it again and commited it.

But now when i changed the file and wanted to commit it it says i cannot find the files in the local _svn folder? A cleanup does not help.

Now as i only made a small change i decided to check out my project again make the change again and commited it now its ok again.

What could have happened here? How can i prevent it from happening again?