I was able to fix the problem. I had to disable SEF in the site config to get all things online again.

Try to use JoomSEF in the next step...

Need help...

After installation of JoomSEF 4 I get for all pages except the startpage a 'Not Found' error. I checked the .htaccess and it seams to be correct. After uninstalling JoomSEF again, the error is still there :(

Thanks for any hints and tips

Richard