Okay, I apparently fixed it - the cause for my troubles was that I followed the installation instructions in the book: 'Running Weblogs with Slash'. The author has the reader create a 'slash' account under a 'slash' group - somehow this seemed to work for him, but did not work for me. Hope the guy is reading this thread, because I've wasted 2 days on this, which I never get back ;-)
Anyway, I'm in business for now - special thanks to shane and Alessio for trying to help :-)