MailItem.Save for "Reply"

Hi,

When handling NewInspector event,
I use MailItem.Save, to save changes.

I encounter the following problem:
If the mail item is an item for "reply", I get the following
error\exception:

Type : System.Runtime.InteropServices.COMException
Message : The messaging interface has returned an unknown error. If the
problem persists, restart Outlook.
Source : Microsoft Office Outlook
StackTrace : at Outlook._MailItem.Save()

The error occurs only when the inspector is opened for "Reply".

I use: Windows XP, Outlook 2000 Object Model , Outlook 2003, C#.

Any reason why this happen ?
Thanks for any help.

Si.