Ok, here is the case...
I installed MP2 (the instruments that is) on an external disc connected to my Mac, because I did not have enough space on the Mac itself anymore. But I have also used that disc on a PC for other things, NOT sampletank or MP2.
When i started Sampletank (or MP2), the instruments showed up twice in the instrument list in the interface. But one of them had ._ in front of their name. When I clicked on an instrument with ._ in front of it, I got an error message about that the instrument could not be found. So i tried to search for those ._ files on my Mac, but they did not appear in the search results. Nor did they show in Finder.
So after advice from Dark Star (I think he is called...?), I brought the disc to work and connected it to a PC. And there the ._ files DID show up in explorer. So I deleted all the files that started with ._ on the PC, took the disc home again, connected it to my Mac and pushed refresh in the interface. And then all the "instruments, that were not instruments after all" disappeared from the instrument list.
I have no idea why all those ._ files showed in the interface or why/where they came from in the first place, but they are gone now. And everything works like a charm!
And what a FANTASTIC library MP2 is! Too bad you have to pay 100 dollars extra for percussion instruments, which I think should be a natural part of the library. But apart from that, I am having a blast
So that is the story.
Regards,
Peter