I get a 500-error when I post a comment on a news article, but not on images and albums. What can the problem be?

Try a standard theme, if it works there you did something wrong with your theme. Please follow this with all further issues. You will surely understand that we can't really help you fixing your customizations.

Yes I realize that, sorry. I compared all the new and original files that are assosiated with the comment form and news page and I managed to fix it. But I still get a 500 error when editing the comments: /zp-core/admin-comments.php?action=savecomment

Can it be that bug which comes from renaming news and pages? (http://www.zenphoto.org/trac/ticket/1244) Because admin-comments.php are original and on line 296 and line 310 it asks for "news" and "pages". It doesn't work to just rename them though.

Well, you can install the nightly build and see if that fixes the problem.

Yes it did:-)