Why do I get this error message?
Another possible cause: If you have an svn-remote..rewriteUUID config set, git-svn may have trouble locating the right meta-data for the repository. For example, you might have something like this (see the git-svn man page for a discussion of why you would want to do this):
[svn-remote "svn"]
url = svn://read-write.test.org
fetch = trunk/project:refs/remotes/trunk
rewriteRoot = http://read-only.test.org/svn
rewriteUUID = 1234-abcd
... where 1234-abcd is the UUID of the read-only mirror. When you 'git svn fetch', you might end up with this file:
.git/svn/refs/remotes/trunk/.rev_map.5678-dcba
... where 56780-dcba is the UUID of the read-write repository. The fix is to:
$ mv .git/svn/refs/remotes/trunk/.rev_map.5678-dcba \
.git/svn/refs/remotes/trunk/.rev_map.1234-abcd
Can't say for certain whether that is a durable solution, i.e., it might get confused next time you 'git svn fetch'. Might try a symlink rather than 'mv', I haven't experimented with that.