RepositoryBrowserPage in fckeditor module can be configured in order to browse multiple repositories (actually website and dms). The configuration of "browsableRepositories" is however a list of tree names, and the RepositoryBrowserPage assumes that the name of the repository always matches the name of the tree.
For example there is no way to configure a "website-jcr" tree since it will look for a "website-jcr" repository too.

It should be fixed by using TreeHandlerManager to get the correct repository name from the tree handler name.