Greg,
I've not tried what you are doing on Win64 so I'll not be of much direct help.
I think that the script editor is a customized version of one of the sample editors that come with the Cypress package.
IIRC Cypress supplied a couple of different sample editors for use with the package.
If you go here
http://www.cypressinc.com/techsupp.htmyou can DL demo.zip - inside are Edit42.zip, sdkSded.zip, MFCSdiEd.zip and vbEnEdit.zip - which I think are the sample editor sources.
I don't remember if the exe files are included or if you'd have to compile the sources.
I'm thinking you could try the sample editors to determine if it is the base code or the mach extensions that are the issue.
Btw, I'm curious, are you running Mach as a 32bit app directly under win64, or are you having to run it in an XP compatibility box (which uses a CPU mode that not all CPU models have)?
Dave