A non valid Add-in with Microsoft Outlook and returned emails.

[kenken45]

Every time I start Microsoft Outlook I get a message saying ‘C:\WINDOWS\Application Data\Microsoft\AddIns\’ is not a valid Office Add-in.
I also sometimes get “failed mail delivery” emails returned to me that I have not sent. Maybe a couple per week. I have also had a couple of virus-infected emails deleted by me AVG antivirus program in the last few weeks.
I tried unchecking the Add-Ins listed on the Add-In Manager in Outlook but it made no difference. There were three: a Net one, a Windows CE one and an AVG antivirus one. Even with all three disabled I still got the message.

I then clicked on the COM Add-Ins button to check this and there are none listed, however, I get the error message again. Also, the top line of the blank screen is actually two blank spaces and the rest of the line is surrounded by greyed dashes. It is as if there is an item there that I can’t click on or anything. If I press the Add button on the COM Add-In window I get an empty folder but get the “not valid…” Message when closing it. It there something hiding in the Add-Ins folder, I wonder. I tried displaying hidden files, etc. but still nothing shows up. Seems a bit weird.
Any ideas or suggestions about how to stop the “not valid Add-In” message would be appreciated.