Paul, it could be one of two things:

1.  You are using external morph targets.  If so uncheck this in Poser's preferences.  I doubt this is the problem however since you have successfully imported other characters.

2. Your Simon character is using compressed .obz files.  I don't think Vue can deal with these at all.   Go to the Poser Python menu and use the uncompress utility to uncompress the folder containing the Simon cr2's.