problem solved by changing rights on htaccess file as above:
… i changed the htaccess file permissions (CHMOD) to 644 and then all was perfect ;o)
choose ‘show hidden files’ in your FTP-client to see .htaccess
before that i tried to solve the problem by deleting the option_value “/%year%/%monthnum%/%postname%/”of permalink_structure in wp_options under myphpadmin – without any effect
many thanks