bb - I'm posting the attached image because it shows not only the values of the variables set in the vssMainButtons script (you're not an idiot, just a human), but also the title bar immediately after I clicked the Synchronize button.

Poser is replacing the "/" delimiters in the path that we assigned to the button with colons. You said "(I don't want to use a "poser" style portable path), since that only works if the item is in your runtime." There we have it, I think.  

I presume that the Windows "" path-delimiter does not get replaced in this way, which is why it works on PCs.

The next step is to determine at what point this is being done... when the path is assigned to the button, or when the button is clicked. but I'm not sure how to go about doing this. In any case, it's a Poser Python bug for sure.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)