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
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators