Editing Page results in template crash

http://www.business.andreasorthen.de/?page_id=12
release wp 1.5.1
Dear all!
What I did:
Editing the page “…business”. Inserting my email with <a href="mailto:<?php the_author_email(); ?>"______</a> twice.
pressed button “edit”
Viewed page
The default template is completely out of shape. Content is missing.

What I checked:
I checked for similar entries here.
I removed both email links and edited again. Same result.
I produced an alternative page “..business” and copied the content to this one. Same result.

What can I do next?
Many regards
Andrew