Thanks for getting back to me.  I followed all the instructions apart from
filtering out the logout URL as I couldn't figure out how to do that.  So of
course it didn't work.  

I am not sure which filter term to use for the logout URL as my java skills
are pretty much nonexistent, and I notice that there may be issues with
cookies too.  I shall re-read the help files, try again in a day or so (once
my brain has unscrambled) and report back. Thank you for your help so far.