Sony Ericsson K750i

I would try to resend the settings to my device via the sonyericsson website. Just go to the support section of thier website. Also, if that doesnt work try a master reset as that sometime help. If that doesnt work, try updating the firmware by again going to the support part of the sony ericsson site downloading the update tool. Then just run the sony upadate process and it will upadate your phones software. If again that doesnt work go to your local service center and have it flashed over there. If you dont have a local service center in your area, check my profile and im sure we can help you.

Sounds like the security in the network settings are messed up somehow. I know that when you send or recieve attached pictures, the network of your carrier(even if it's pre-paid you still have a carrier) has to scan them for security, they can only be a certain size, and or a certain format. Here's an answer that could(and most times does) fix the problem. You are going to a Phone Reset it's also called a Manufacture Reset. Call you carrier and ask them to assist you. It should take only a few minutes to complete. The downside, any pictures, messages will be deleted. One more thing, you may be thinking, "When people send a picture in a message, I don't have the same problem? I would say exactly. There are different rules when it comes to "Attached files, or pictures".