Xfs request 'GetHdrEntry' failed. Response code: 'MsgNotFound', server resp

HI, My brother has just sent me a query. His comp is running W7 and he uses Outlook for email. When he sends an email this is displayed on his screen:
[Xfs request 'GetHdrEntry' failed. Response code: 'MsgNotFound', server response: '650 0']
The email is sent and the recipient (me) receives the email as normal.
Has he got a problem or is there a way to remove/delete the Xfs request message?
I use Mozilla TB and I don't have any problems. Neil.

I've been looking through MS Community Forum and Outlook .com does not have an answer to many users who are experiencing this message when sending emails. Some have had the problem disappear a couple of days later, but many have not received any help from Outlook.com. Some get another message asking if they would like to contact MS about their problem - but no link is provided to do this.
I think I'll advise my brother to use Mozilla. Neil.

 

Update: I ran Seagate Seatools on the HardDrive and it failed the tests. So as no-one had an "fix" for the message, I will close this Thread. Neil.

 

Thanks Arie. I had carried out a Malwarebytes scan which came up clean and then his comp Blue screened and restarted. He then told me that the comp had been doing this on and off since he purchased it 2nd hand about 5 months ago.
That is why I carried out the Seatools test.
It was originally running XP and the previous owner had installed W7 Home Premium before advertising it for sale. My brother did not consult me before he purchased the comp. He paid $190.00 for it with a monitor and proudly showed me his purchase when he called in on his way home.
He didn't get a DVD with the OS and the Audio didn't work initially. I had to help him locate Lenova drivers to get the sound working. He now has a piece of junk and has to decide what to do.
Lesson learned - seek advice before plunging in - or you will drown. Neil.