Hi Sebastian! Check your lighttpd configuration, especially 10-cgi.conf. Here's mine:
## BackupPC Web Interface alias.url += ( "/backuppc" => "/usr/share/backuppc/cgi-bin/" ) $HTTP["url"] =~ "^/backuppc" { cgi.assign = ( *"index.cgi" => "",* ".cgi" => "/usr/bin/perl" ) } * Corvus*