The first thing to do when troubleshooting Menalto Gallery2's problems is to clear its cache. This is because Gallery's cache causes strange problems such as blank pages.

The best and most reliable way to clear the cache is by going to the following URL:

http://yourdomain.com/path_to_gallery/lib/support/index.php?cache

There you will have to provide 'Gallery setup password' which can be found in the file config.php located in the main Gallery directory. Once you are authorized, make sure all checkboxes are checked except the one for 'Thumbnails and resizes'.

Proceed with clearing the cache and see if this solves your problem. If not check to see if there are upgrades for your Gallery version which may fix a bug you are experiencing.