“general mail failure” when trying to send attachment in Excel 2003

When an Excel 2003 worksheet is open and the option File/Send to/ Mail recipient ( as attachment ) is taken the error message “general mail failure” appears. The user in question is using a Windows XP SP3 desktop with Office 2003 SP3 installed in a Microsoft Exchange environment . I have tried these fixes which I have found on the internet without success:-
(1) detect and repair
(2) uninstall and reinstall office 2003
(3) fixmapi.exe
(4) rename mapi to mapiold and restarted the application
(5) rename Excel.xlb and restart the application .

The user’s mailbox is not full and I have turned off Windows firewall just in case this might be causing the issue issue. Has anybody any other suggestions ?