Can not save modification of subject in mail on outlook 2003

Dear All
When i try to change the subject and save it on of either mail on outlook
2003,it's error warning as the mentioned "The item could not be saved because
it has been changed by another user or in another window.Do you want to make
a copy in the default folder for the item?".And,that's remind me with the two
choices of "Yes" or "No".
If i press the "Yes" button,it will new another item on outlook as just
modification,BUT,the original item of mail is still existing on outlook.If I
press the "No" button,it will be canceled,and nothing is changed.
The First,I had tried to reinstall the outlook program and rename office on
registry ediotr - HKEY_CURRENT_USER - Software - Microsoft,but the problem is
still with.
The sencond,I had tried to install the hotfix "officexpkb837007enu" by the
path
http://support.microsoft.com/hotfix/...=en-us.But,the problem is still same as before.
Another,If the mail item of subject ever be changed,It's nothing problem of
second modification on subject of the mail.
Would you please kindly to check what's the cause of problem?
Hoping for your kindly reply.Many thanks.

Br
Komi Fung