Import function not work

I have installed guestbook module and drupal guestbook module.

If I want to import the guestbook modul entries:

Table 'dbdrupal.dgb' doesn't exist query: SELECT count(id) FROM dgb in /htdocs/drupal/sites/all/modules/dgb/dgb_import/dgb_import.module in Zeile 79.

and

Table 'dbdrupal.guestbook' doesn't exist query: SELECT count(id) FROM guestbook in /htdocs/drupal/sites/all/modules/dgb/dgb_import/dgb_import.module in Zeile 105.

By the way: I am using table_prefix in my drupalinstallation database.

What runs here wrong?

Many thanks and greetings
Frank