Apple Mail has stopped downloading new mail
I have got 4 different iMap Mail accounts, 3 of them GMail and one MobileMe. Suddenly on my MacBook Pro Mail has stopped downloading new mail to one of the GMail accounts. I can send new mail and it appears in the Sent folder. If I go online to GMail in a browser it is fine, and also it works fine on a Mac Mini I have that was originally installed using a clone of my MBP installation. It also works fine on my iPhone and iPad. I have not fiddled with any of the Mail preferences. How can I get to the bottom of this ?
13, Mac OS X (10.6.7)