HELP!!! Handcent Group Messaging

Greetings Benevolent Handcent Experts:

I'm wondering how to send a text to a group of ~500 people, on my Samsung Epic. Here's what I've tried:

Created a Google group
Compose the message
Go to the "plus sign" at the upper right
Select "Group"
Select the Group I want to send the message to (either by the checkbox on the left, or the arrow on the right/menu/select all)

What happens every time: a "Please wait, checking all contact" message pops up, then I'm returned to the composing screen. NO contacts are entered in the "To" field.

How do I make this work? Thanks in advance,
G