I've looked over and done all solutions discussed on this site about this problem. Nothing seems to help.
I'm running XP with Outlook 2003 and I can send text messages fine, but when I add an attachment I get an error message and message doesn't get sent. Not all the time though, but most of the time, it is not consistent. I used to be able to send attachments fine, but out of the blue this started happening, I was Originally running outlook express and thought I maybe needed an update, so I bought Microsoft office and still same problem. I deleted all my emails, that didn't help.
I've tried changing settings(timeouts, 10 minute), I've uninstalled Norton professional 2004, I've added all microsoft updates and service packs. I use my modem to connect to dial-up internet, my service provider said everything is fine on their end.