Missing keyword library during export

I am not sure if this is a real Mac issues, but because I have after moving to Mac I will post it here:

I moved my keyword libraries from a Windows installation to a Mac installation. Working with keyword libraries goes without any issues, meaning the new installation shows my libs, adding keywords to my pictures works fine etc.

Now, during export, I run into troubles: I want to exclude certain libraries during the export and therefore I try to exclude them in my receipe. The libs are shown in the list but for any reason when I select one or more, C1 says "uncheck missing libraries":
As I said: The libs are there (otherwise C1 would not be able to show the list) and I can use them to generate keywords.

First I thought that this is related to the fact that I copied my receipes from the Win installation as well and therfore some physical file reference would fail. But the above mentioned problem also occurs if I try to exclude some libs in default receipes that are coming along with the C1 installation.

Any idea why?