I have the same problem today, Frank. Received an MMS message with a photo, after it downloaded and I clicked the message a pop-up came up "A read receipt will be sent, Yes/No" I clicked Yes thinking I had to in order to view the message. Suddenly now that "text message not sent" notification keeps popping up.
I've deleted the original message/photo, rebooted the phone (soft reboot, on and off) twice, even cleared the messaging and SMS cache in the Applications settings, no luck.
I saw a similar post from almost a YEAR ago for the Droid X forum on line, and there was talk about 3rd party SMS applications like HandCent that when loaded allowed access to the "unsent messages" queue. But I never had any SMS app other than stock, and I really would rather FIX the problem than work around it!
Seems the only answer those folks got from Verizon was (wait for it) "Factory Reset."
Now I know there are some Verizon techs on this forum, but since I've gotten MY G2G, I've heard that mantra over and over from Level 2 Techs - "Sorry, sir, but you'll have to perform a factory reset." Why cannot we FIX the problem?
Sometimes...only sometimes mind you, I wish I had bought an iPhone (shiver).
Anyway, hopefully someone will notice this thread and give us some insight.
Thanks for posting Frank.