There is a workaround for Windows Publisher not logging into the Gallery.

It appears as though logging into the Gallery directly via the Windows Publisher does not work properly and you will be asked to login over and over. The current workaround is you must login to the website and enter the Gallery prior to attempting to upload photos using the Windows Publisher. You will then be able to properly use the Windows Publishing Wizard with your Gallery albums at Messinet Secure Services.

This information is available in the Help section of the website or wiki.