If you received this error code on an inbound message, there was a failure attempting to receive an incoming MMS, as your Twilio phone number was sent an MMS in a region where Twilio does not support incoming MMS.
If you received this error code on an outbound message, the destination handset either doesn't support MMS, or MMS is not currently enabled on the device.
For Inbound, it is recommended that you respond to the user sending the MMS to let them know that you cannot receive MMS in this region.