Hi
Welcome to WW. Not meaning to burst your bubble or anything, but the first thing I'd check out is if this agency are planning to charge you anything for 'turning your novel into a screenplay'.
Secondly, I'd check what Preditors and Editors have to say about this agency.
http://anotherealm.com/prededitors/
An indispensible guide to the industry.
It just seems a little strange that they would reject a fiction novel MS but offer to rework it as a screenplay. I hope I'm wrong, but you can never be too careful.
Best
JB
<Added>Sorry, I just noticed they haven't rejected your MS or even seen it. I think that makes it even stranger.