Got this problem after updating to 2.1 today. Initially no plugins were activated and everything was ok. The tried Sidebar Widgets, and they worked. But after uploadinh Live 0.4 plugin, WP plugin page doesn't open anymore (just tries to load endlessly).
In despair set wp-contents/plugins recursively to 777. Nothing.
Reuploaded plugins - nothing.
Reuploaded plugins.php - nothing.
Outta ma wits... Please, help.
P.S. The same plugins with 2.1 work splendidly on my own testbed PC.