constant Outlook for Mac 2011 error message

I have an imap account on an external server, I have had this account for years but recently I get the following message coming up:
"mail could not be received at this time:
the server for account returned the error login failed your username password or security settings may be incorrect would you like to try resetting your password"
Despite this message I do receive emails, but this message continues to come up every few minutes. I know that my password and user name is correct.
I have tried setting authentication to: 'Use incoming server info', as well setting it to: 'User name and password' - neither fixes the issue.
I've selected 'Use IMAP idle"
Under 'digital signing' I've selected 'none. Under 'encryption certificate' I've selected 'none'.
When I contacted the support for my server the response was: "The error you are encountering indicates that you are most likely timing out on the automatic login in the email client. That is why it will have inconsistent results. This may be caused by your firewall or antivirus."
I have no idea how to fix this issue. Any ideas would be VERY MUCH appreciated! : )

If no-one knows the answer to my above issue can you suggest any other areas or forums I should post on?

I really don't know what to do, and the constant error message popping up is driving me crazy!

Why don't you try re-setting your password? I have had the same problem occur with my gmail account and re-setting the password fixed it.

As far as support for Outlook 2011, the best place to go is directly to the Microsoft sponsored forums. Here is the LINK.