I've found that GroupSMS doesn't work on some Manila 2.5 roms, as the SMS client only allows up to 10 recipients (though this can be changed to 50).
Also, when the contacts are imported by group SMS, they are 'invalid' recipients according to the manila 2.5 client.
Not sure if this is fixable, but it'd be much appreciated if it were.
I must say, this is the first time I've had an issue with group SMS (which is probably the fault of the M2.5 client, not group SMS), and I've been using it for I guess around 2 years, every week, and it saves me probably 10-20 minutes every time - fantastic!
Thanks so much for the work on this very useful software - it's one of the main reasons I won't move to an Iphone.
Cheers!