The autorevision.exe code was changed sometimes back. Earlier autorevision.exe used to find out the revision number using a fallback code in case svn.exe was not found. But the latest code doesn't have that fallback code and now solely dependent on svn.exe.
So in short, if autorevision can't execute svn, the revision number will be displayed as zero. Please check your path again and download a latest copy of svn.