Hey there
I’d be happy to help with your MMS issue! The error message you’re receiving is due to the app or service crashing. Depending on your device make/model, I would recommend trying to power the phone on in Safe Mode if available and test. If the MMS works while in Safe Mode, we can be sure this is being caused by another app, which would need to be uninstalled. If the issue persists in Safe Mode, or you cannot use Safe Mode, I would recommend backing up the device and performing a factory reset.
Another test would be to use an alternative messaging app such as Google Hangouts to try sending an MMS. If that works, this would also indicate an issue with the default messaging app.
I hope this helps!
Charise