Do you have Gallery installed? Because the redirect to /install also includes this message:
Text Formatted Code
<b>Fatal error</b>: Call to undefined function: galleryinitfirstpass() in <b>/homepages/18/d89588739/htdocs/gallery/modules/core/classes/GalleryEmbed.class</b> on line <b>80</b>
Looks like you've somehow messed up your Gallery install. Try disabling it (or if you know what that message means - fix it).
bye, Dirk