I finally managed to find a solution on my own... on a Spanish website! Geez...
This might help someone else, so here's where I found a hint to help solve:
From what I understood, the plugin tries to create tables in the form of a standard WordPress installation, in which tables are named with the suffix "wp_".
However, in my case (and probably others), I have multiple Databases and some with other WordPress installations, and so the prefix isn't the same for all. The prefix for this particular WordPress Database is "mob2_"... and so, the plugin couldn't create the tables in the form "wp_" and therefor couldn't find his tables after activating the plugin.
So what I did was to copy the entire CREATE TABLE codes in the link above. Then I went to phphMyAdmin to find my database. In there, I sent out the query. All tables were created successfully. I then renamed the tables changing prefix "wp_" for my own "mob2_".
After that, my plugin still gave me the error, but all the gallery menu worked. So I deactivated and reactivated the plugin.
Error gone :)
Hope all this is clear and will help someone else!