My phone is an LG Fortune 2. I can send group messages in small groups, but not large ones. I still receive what others send in the group text, but I can't reply. It is totally updated.
Assuming you are talking about SMS/MMS messages, the number of recipients is limited by your carrier. All use a relatively low number (10-25) with ATT being one of the lowest.
Which texting app are you using?
What is the exact wording of any error messages you are getting?