Hi there.
I get that message when trying to get into a Blitzkrieg, but, obviously, not with a SS (at least I don't know any event SS). I try it with my Danton, a EBB.
This question might be pretty stupid, but I want to make sure that it's just a typo, because in the Blitzkrieg's description it says that SS aren't allowed, but nothing about event ships.
Thanks.