Handcent Settings and Warning Sign

[rspiet]

Why does Handcent show a warning sign (white ! inside of a yellow traingle) next to some of my threads.

I want the ability to text similar to how I e-mail where I have the option to send and reply to group threads (Reply All) or just reply to the sender (Reply). What settings do I need to have set? This is why I don't use the stock app on my galaxy s3.