[Svnmerge] Initialization problem

[Wayne]

I am trying to setup svnmerge on a project I am working on. We created a 
branch some time ago but did not run svnmerge init at that time. Now we 
want to start using svnmerge. I ran svnmerge init on my branch and it 
seems to have done the right thing. I see an 'svnmerge-integrated' 
property with '/branches/my_branch:1-4' I think this is correct because 
I did create the branch at revision 4 of the repository. However when I 
try to run 'svnmerge avail' I get the following error message:

svnmerge avail
svnmerge: command execution failed (exit code: 1)
svn --non-interactive propget --strict "svnmerge-integrated" 
"http://xxx/branches/my_branch"
svn: 'http://xxxx/branches/my_branch' does not exist in revision '68'

(I removed the repo path from the message and also changed the branch name)

Revision 68 is where I checked in the merge info created by svnmerge init.

Is there a way that I can fix this? Last night I played around with a 
dummy repository just to see how things work and I can't figure out 
what's wrong.

Thanks.