Plugin not working properly on network

Hi,
I’m using your plugin on my network and it was working fine on one of the websites.
I went to set up a quiz on the other website in the network, and first it didn’t save the settings, then it gave me an error message for both the settings and the Watu quiz sections.
See below:

Errore sul database di WordPress: [Table ‘ellyph_wrdp1.wp_watu_master’ doesn’t exist] SELECT Q.ID,Q.name,Q.added_on, (SELECT COUNT(ID) FROM wp_watu_question WHERE exam_id=Q.ID) AS question_count, (SELECT COUNT(ID) FROM wp_watu_takings WHERE exam_id=Q.ID) AS taken FROM wp_watu_master AS Q ORDER BY Q.ID DESC

And:

Errore sul database di WordPress: [Table ‘ellyph_wrdp1.wp_watu_master’ doesn’t exist] SELECT ID, name, no_ajax FROM wp_watu_master ORDER BY name

Can’t seem to get back to the default pages, what do I do?
Thanks!

Elisa