Hi all,
Thanks for everyone's help, especially RR!
I eventually got there through trial and error. I'm still unsure exactly why, but URL encoding the original DOCID in the GET that searches the folder, then on the GET that retrieves the document, do not URL decode, and replace any <space> with a + sign, seemed to work. Again, I'm just not familiar enough with HTTP encoding to understand a straight forward decode didn't work. Also the removal of the + and the insert of the space is odd.
So a combination of the string manipulation and the getOpenDocId(), appears to be the final solution.
Regards
DB