That is a limit from Facebook, and it's impossible for us to override. That number is determined by Facebook based on a variety of factors including the current user, the app itself, how many invites are normally sent from the app, how many invites are marked as spammy, etc. 30 is about the max we've seen, so there's nothing 'wrong' with your app, it sounds like.
We're currently using the Requests 1.0 system from Facebook, but are investigating the Requests 2.0 system which has an increased invitation limit (up to 100 I believe). We're shooting to have that system in the 4.1 release due out later this year.
Hope that helps, and that it's not too constricting as it is. Glad you're enjoying JFBConnect overall though!
Alex
JFBCInvite Module limitations
