Cannot "create" Time Machine backup service
I have Mac OSX Server v 5.1.7 running on a Mac mini (2.7Ghz core i7, 8GB RAM, Mid-2011)) with OSX El Capitain (10.11.6).
When I try to add a folder to use as the destination for my Time Machine backups the 'create' button on the following screen does nothing!
How can I diagnose what the error is (if any?) and how can I work around this?