I have to import an huge SVN repository that I have to transfer from one server to another. So I exported it from the old server:
svnadmin dump . > archive.sv
Have you changed the server version? This is a known issue in 1.6, and causes problems when going from 1.4 or 1.5.
Subversion 1.6 no longer accepts carriage returns (^M) in property files. You'll need to fix the line breaks in your svn:ignore file(s), or recreate if that's easier.
Alternatively, you could go for Subversion 1.7, or use uberSVN.