I would guess that it is a WIBU driver version thing. See:
http://www.graphisoft.com/support/archicad/downloads/WIBU.html
perhaps you need to reinstall 5.20b
(For OS 10.6, the converters work with the 5.3 and the wkmac.lib listed there.)
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB