Hi Paul,
yes, I did a restart - but it didn't solve it, but good news, I got my pc to take me back to an earlier build of Windows 10 [I was very worried files would disappear], and Sibelius, Vienna Instruments and V Ensemble all work now in Sibelius and Cubase.
I did a reinstall of Vienna Instruments Pro and Vienna Ensemble, and checked that these still were able to load and play in Cubase, and they did with no more missing .dll problems.
The only thing I cannot get working now is Vienna Pro standalone. It keeps crashing on me when I start it, but at least I can get it going in Sibelius and Cubase.
I don't know what on earth caused the missing .dll files, but I think I 'll stick with this particular past Windows 10 version for a while.
Thanks for getting back to me Paul. I'll do another restart and check if the standalone version will work after reinstalling it again.
best,
Steve :-)