Imagesource of char not working as expected in Windows

[David Glasgow]

RevRunners

I capture, save and display within a scrolling field ("results") a series of screenshots as follows:

put specialfolderpath("temporary") & "/evapics/image" & the secs & ".png" into tdest
export snapshot from rect trect to file tdest as PNG
set the imagesource of char 1 of last line of field "results" to "binfile:/" & tdest

The character referred to is a tilde (~ or wiggleworm, if you prefer common usage) placed in the field a tad earlier.  On OSX , this works OK.  However, testing a standalone on Vista produces a results field displaying tildes but no images.  The images are being save to the temporary folder, so the path looks good and I am not falling into the virtualisation heffalump trap.  

I have studio for Mac, so can't debug this.  Any suggestions re what might be going on?

David Glasgow