Ditch it and move to netbeans :-)
I could never get the RadRails debugger to work reliably as it used to trash Windows.
Sounds harsh and RadRails is a superb tool (I only ditched it a month ago because it was causing system lock ups) but after playing around with netbeans for the last 4/5 weeks I found it much more responsive, never crashes and I have been totally blown away by the whole experience.
I honestly thought that RadRails was cool (and it is) but netbeans is in a totally different league.
The debugger is awesome compared to RadRails and allows you to easily step through the code but I have found that I need to do this far less as the context sensitive help in the code editor is just so totally brilliant that I just don't make the same stupid mistakes any more.
Seriously you have to try it to understand the difference.
I still haven't uninstalled RadRails but I miss nothing and have only used it once since I set up netbeans.
Sorry that doesn't really answer your question but I hope it is enough for you to at least find a better and easier alternative.
Debugging at the click of a button rocks. Not needing to debug as often ROCKS even more :-)
What you want and what you need are too often not the same thing!
When your head is hurting from trying to solve a problem, stop standing on it. When you are the right way up you will see the problem differently and you just might find the solution.
(Quote by me 15th July 2009)