(I am replying to myself)
Hrm, i also get the same error with a non-CVS 0.90 gem... sorry for asking on the list too quick, found this posting from jamie, seems to be sth more complicated.
http://lists.puredata.info/pipermail/gem-dev/2005-04/000937.html:
...hmm, this kind of stuff keeps coming up and reminding me that we have to do something about this :-)
regards, P8r