Membership won't load subscribe button on multisite

Hey guys,

I just moved Membership to a brand new multisite network installation (2 sites with domain mapping).
Everything works fine, except the subscription buttons - the only show up on my main site.

I set global tables true, but this doesn't change anything - only difference: The admin menu is now integrated into the admin panel of the main site. Without global tabels, it is integrated into the network administration area. In both cases, it doesn't show up on the second site.

I also tried to track down the problem, and found out, that on the second site, the plugin isn't even able to check the payment gateways.
Again: Everything else (e.g. Access Levels or even the subscription form) works just fine on both sites!

Any ideas, what to change or where in the code I need to make changes.