SVN Error: post-commit hook failed with locked file message

I get the following SVN error (using TortoiseSVN) when i am trying to tag trunk.

Error: post-commit hook failed (exit code 1) with output:  
Error: svn: Working copy '.' locked  
Error: svn: run 'svn cleanup' to remove locks (type 'svn help cleanup' for details)

The tag still seems to have been created ...

I have no post-commit hooks added ...

I have tried the following:

1. update + cleanup
2. search for 'lock' files in .svn dir
3. fresh checkout

I am not sure what is going on, any help would be appreciated?

Earlier I changed "svnserve.conf" realm = [new-realm] which caused user/pass re-prompts for checkouts/updates. On the SVN server there is a post-commit hook which does an svn update, because of the realm change, the hook was dying because creds needed to be reset.

Moral of the story is: changing realm will cause creds to be invalidated (which may break your automated scripts)