I tried to replicate your mms issue with my xtrROM 3.0.3 with no results (that is, the pics send with no errors or other problems).
I'm thinking that a re-flash might be the way to go, but before doing that I'd check to be sure that I had not messed with a setting in MMS connection settings.
Also, make sure wifi is turned off before sending an MMS to see if that helps (be sure to reboot after turning off wifi and before attempting to send a message).
But if that were happening to me, I'd back up gmail, calendar and apps and re-flash the ROM. As always, I'd even re-download the zip to a PC, not my phone and not a laptop just to eliminate possible problems with the zip.
Then re-flash.