i solve this problem.
yes, this reg-cleaner thing is basically when you have error. when you are using drupal, it has something to do with the .htaccess configuration. in particular, the friendly url setting.
don't bother to look for .htaccess configuration. this is what i did (not sure it is the best way, but it worked):
1. go to configuration and clean urls and disable it.
2. go to module and turn off the pathauto module.
3. go to performance and clear caches.
4. do the export/import database again.