vis plugin missing from list in Win7, does appear in XP

[ForestCat]

I grabbed the Milkdrop source and compiled it, and copied it to the plugin folder. The plugin is available in the list of installed vis plugins on a v5.6.6 install under XP, but does not appear in the list under win 7. Anyone have any idea why that might be happening?
I've tried this on a few different computers.

Thanks