Unable to send/receive mms


ZTE Mustang - rooted - I am unable to send or receive pics messaging. When i send i get error message "unable to send." At first it was also giving me "try recording in mms mode" which, i found, from all my searching thru my phone, is not a mode or option. But i no longer get that message. when someone sends me a pic message an error message used to say "unable to download. no subject in subject line." but now it just says "unable to download. retrying. .." and it will retry unsuccessfully until i delete the message. any ideas about what to do about this?