permissions and packed-refs?

This is likely a really stupid question... a repo that was working, has now stopped accepting a push with

Counting objects: 43, done.
Compressing objects: 100% (18/18)   Compressing objects: 100% (18/18),
done.
Writing objects: 100% (23/23)   Writing objects: 100% (23/23), 4.65 KiB,
done.
Total 23 (delta 10), reused 0 (delta 0)
error: Unable to append to logs/refs/heads/realtime: Permission denied
Pushing to ssh://10.1.3.153/pub/scm/git/git-svn/realtime.git
To ssh://10.1.3.153/pub/scm/git/git-svn/realtime.git
 ! [remote rejected] realtime -> realtime (failed to write)
error: failed to push some refs to
'ssh://10.1.3.153/pub/scm/git/git-svn/realtime.git'

I think git gc was run on the server at some point, as the head in question has been shifted into packed-refs.

Server is linux (1.5.4.4) client is msysGit.