Thanks Marc, not sure I want to go there yet since it creates additional clutter.
I'd rather find out what the problem actually is.
For the time being, I use the Qt4 version from yesterday.
malbrechtHm - I went through my user and system paths and didn't find any python or Qt related entries, not sure where else to look. I don't have python installed separately.
The most likely issue to me seems to be a Python hickup. Do you have some global Python ENV VARs that might interfer with Houdini's Python? H is using a packaged 2.7, but it may well be possible that it tries to use your installed 3.x or whatever - and fails.
One thing you could try is set up a clean user (assuming you are setting environments for users, not globally for administrators) and check if H16/Qt5 works there. A virtual machine with a clean Windows install also comes in handy to have a quick go at comparing setups.
Else the best thing you can do is send your report to email@example.com - they may be slightly drowning in requests right now, so cut them some slack