I asked someone more familiar with Rail Analysis, and they advised that in order for the menu pick for RA to be un-greyed, a Power Grid Library needs to be generated. In order for a Power Grid Library to be generated, first go to "Power->Rail Analysis->Power Grid Library->Set Power Grid Library Mode..." then "Create Power Grid Library" then Rail Analysis should be un-greyed.
I wanted to test this before passing the advice along to you, but I didn't have a design handy with the required technology files and layer mapping files.
If your get a chance to try this, please report back and let us know if it resolved your issue.
Hope this helps,
Bob