Okay, bb, I got to the bottom of the problem and I have it working using the vssFolder variable. The following line of code works on my Mac (but it won't work on a PC):

call = os.path.join(vssFolder, self.pyfileFmt % (i+1)).replace("/",":")[1:]

On a Mac, it is necessary to use ":" as the path delimiter for defining buttons - we can't use "/". It is true that Poser 7 converts any "/" it finds into ":", but then it expects to find a file by that name including the ":" characters - i.e. it treats each "/" that it has converted into a ":" as part of the filename, instead of a path delimiter. Crazy.

Clearly the above code won't work on a PC because I am dropping the first character in order to convert it to an absolute path using the ":" delimiter. We could insert an if-else condition: if the first character of vssFolder is "/" use the above line of code, otherwise use the original line...  but I can't think any more about it right now as it's past 2am here and I have to get up at 7.

"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)