When I installed Nextgen for the first time and tried to activate the plugin, I had the dreaded 500 error (common with 1&1 hosted sites) I fixed it with the proper php.ini and the .htaccess workarounds, and when I got into the Dashboard again I saw the plugin was already activated. Cool, I thought, but then I got the “going around in circles” upgrade loop when I access the Gallery settings, that you described.
1&1 support suggested that I deactivate the plugin and reactivate before trying the upgrade and….it worked!
So…Deactivate the Plugin, logout and log back in again the WP Dashboard and reactivate NextGen Gallery. The loop should now be fixed.
