failed to send doc via mapi/winxp?

Answer 1

MAPI is an eMail protocol for sending attachments = so I assume you are asking what might be wrong ?

Prime candidates are your Firewall and the MAPI Server (lack of permissions or file too large are other possibilities).

Did it used to work ?
Yes - focus on what's different between when it used to work and now - eg. what did you change ? - can you change it back ?

No, never worked - well you haven't set mail up correctly - contact you eMail provider / ISP.