Thans for the reply!
I found my problem. What I did was, I deleted the whole wiki incl. database and reinstalled everything. Then I made a new tiki site and compared the database. The only relevant change was in "tiki_pages". Than i imported a single page with "INSERT INTO 'tiki_pages'('pageName', 'pageSlug', 'data', 'is_html') VALUES ('Test', 'TestSite', '
', 1) " and this worked too.
So I was able to call the site via the "pageSlug". Than I imported a test file from our old website and it didn't worked.
The problem was simply... there was a space before and after the pageSlug, so I didn't had "test" but " test ", and that is not a valid URL.
I changed my tool for the export, created new SQL files and now everything works fine! Thank you really much.