Main page does not show albums after logging in

Gallery URL = http://beeldbank.nederlandmetro.nl/gallery2/main.php
Gallery version = 2.3.1 core 1.3.0.1
API = Core 7.54, Module 3.9, Theme 2.6, Embed 1.5
PHP version = 5.2.5 cgi
Webserver = Apache
Database = mysqlt 5.1.30-log, lock.system=flock
Toolkits = Gd, ImageMagick, SquareThumb
Acceleration = partial/86400, full/604800
Operating system = Linux cash.awardspace.com 2.6.24.3 #4 SMP Thu Sep 10 13:08:39 UTC 2009 x86_64
Default theme = carbon
gettext = enabled
Locale = en_US
Browser = Mozilla/5.0 (Windows NT 5.1) AppleWebKit/534.24 (KHTML, like Gecko) Chrome/11.0.696.71 Safari/534.24

Since the past 24 hours, users logging into my Gallery (including me) cannot see the albums on the main page (main.php) when they are logged in. Whenever they log out, everything on the main page displays fine.
Logged in users can see all the other sub-albums and photos just fine, only the main page remains blank.

I cannot remember having made any changes to the file or database structure over the past 24 hours, except for some regular db maintenance like table optimization, or deleting the database and template cache via the Maintenance module in Site Admin.

This is driving me nuts...anyone familiar with this problem and with a solution?