HTTP-500-Error after installing, configurating gallery-modul

Issue Summary

I installed Gallery2 of menalto (Path: drupal/gallery2).
I created a standalone database for the gallery2 - I hope this is correct?!
On gallery2 I configured and activated the Mod_rewrite-Plugin.

I activated the Gallery-Modul in Drupal. Then I configured the CleanURL under Drupal.
Under admin - settings - gallery I click on Reset/Restart and then the path auto-configuration.
In step 4 when I click on "Configure URL Rewrite Plugin" I get a blank Site on Firefox-3.5 and a http-500-error on IE8.
After this I can`t get the admin and module site in drupal, theres is a http-500-error too.

I tought the error is in the .htaccess-file in the Mod-Rewrite-Part. But if I disable the Mod-Rewrite under G2 and the CleanURL in Drupal, delete the Mod-Rewrite-Part in the .htaccess-file and click reset/restart in the gallery-modul and skip the url-part I get the same errors.

In both configuration if I reset the gallery-configuration all sites works ok.

Whats the error?!?!