I got into a nasty problem today. While trying to commit the code in a SVN repository I got an error saying "no ancestry information".
It took me a few (good) minutes and some searches on the Internet to find the solution for this problem. It seems that the SVN commit is forbidden if you try to commit a file that is a folders structure, and one of the nodes in it (not the top most parent) is missing the .svn folder.
- folder1 [with .svn] - folder2 [without .svn] - folder3 [with .svn]
Committing "folder3" will bring that error message. Couldn't find the reason for this but, in my opinion, this is because the commit will try to update the ".svn" folders in the parent directories and will find a gap in this hierarchy.