Irfanview opens behind Opus window

I've used Opus 9, 10 in the past and now have Version11. Recently I purchased a new Surface Pro3 64bt computer running Win8 and find that if I doubleclick on a .jpeg file, IRFANVIEW.EXE (the program I use to view photos etc) opens but runs BEHIND the Directory Opus program rather than ON TOP of it as has been the case with my old 64bt computer also running Win8 but using Opus 10.5.2.0.4913.

I've searched Settings on both computers and as they appear the same so I was wondering whether anyone else has experienced the same problem and if so how to fix it.

Thanks

It's probably this: Why are my Opus windows on-top?