Outlook email client

Using the Outlook email client from Microsoft Office 2007 on W7 PC. I have started to encounter a very annoying recurrent pop-up message. It is asking for verification of email address and password on each of the 3 accounts I use. The address and password (as *****) are filled in and no matter how many times I click either Save or Cancel a minute or two later it comes up again, and again, and again!! It's driving me nuts.
I think I recall reading someone else having this problem (can't remember if it was on this forum) and they were referred to a Microsoft explanation and what to do but for the life of me I can't track down where I read it.:(
Any ideas Guys?

Outlook email client