Not a timely response, considering this post is three years old, but as I recently had this issue (geometric network creation was halted midway through, could not create a new geometric network with those objects), I thought I would comment for anyone else that has the same problem.
It looks like that as part of the geometric network creation process, the application will first create a topology object. If the creation process crashes or is halted halfway through, that topology object will remain -but since it is not an expected object, most would just see that the geometric network was not created and not notice that there is now a topology object. That object will need to be deleted before you can start the creation process again, since a feature class can either participate in a topology object or a geometric network, but not both. (And to the deletion issue, you can't delete objects that participate in either until you delete the top level topology or geometric object).
I honestly can't remember what I ended up doing. Most likely I called technical support to resolve it. I do know that I don't have the issue currently.