Subversion - only anonym access possible

setting up a virtual server with subversion works. Creating a user for ftp + subversion works.
Creating a new repo for subversion with the new created user works.

Using the subversion server does only work in anonymous mode. Error accessing the subversion-repo in the browser:

This server could not verify that you are authorized to access the document requested. Either you supplied the wrong credentials (e.g., bad password), or your browser doesn’t understand how to supply the credentials required.

user of the svn-directory is apache, group is the domain-owner
error-log in webmin:

chmod: changing permissions of `/home/openexperts/domains/’: Operation not permitted

(I tried to fix the permissions)

Any ideas what to check further for analysing the problem?

Thanks for the help
Best regards