I believe this might be because the LMC-1 AU is not a universal binary plug-in.
A couple of years ago Mac's went through a big, big hardware transition... from ppc chip to intel. As a result, some applications which were written for ppc mac's only cannot run (or run very slowly on intel mac's).
Many developers updated their software to work on ppc and intel machines. They are given the term "universal binary".
There are other free plug-ins that have not been updated to universal binary and it's my guess that the same has happened here too.
Do email Solid State Logic directly to ask if they have a universal binary version of the LMC-1.
If anyone on a PPC mac (G4 or G5) is interested in this plug-in here is the link: