The only place to unmount safely is:
1. Go to Sitewide admin, select developers admin in the right hand top corner of the page, and select sitemap.
2. Select the the subsite you want to delete, and click on the + if youve other modules installed under the subsite.
3. Remove them first by selecting "unmount" and than delete and repeat this process until all modules are removed.
4. Now you can unmount and delete the subsite.
5. You can not remove modules direct form the subsite admin unfortunatly, allthough the trashcan gives the impression that would work.
That should do the trick and should prevent the error message above beeing displayed.
Good luck
Ben
