Delivery failed: (invalid destination or service blocked at destination)

[calsryan21]

So, my droid has stopped receiving text messages from certain people. My phone had no problem receiving the messages, until one day, the person sending the message just couldn't send them anymore. On the person's phone, the message "Delivery failed: (invalid destination or service blocked at destination)" shows up on their phone. It has not happened to just one person, but actually a lot. Other people can still text me.
I know I'm not blocking any texts from people....so does anyone have suggestions on how to fix this?