Runkeeper on treadmill?

You can enter your run manually using the data from the treadmill. Run keeper won't work in the normal way.

GPS works by your watch/phone/gadget 'seeing' three or more satellites in the sky. If it cannot see the sky, it won't work. That's why GPS is a bit iffy in heavily built-up areas with tower blocks, and by the coast where it can see satellites reflected off the sea.

Just follow Ully's guidance and add the run manually.

As Ully says, the only solution is to enter your data manually at the end of the run, run keeper is otherwise going to think you have travelled no distance.