I'm also seeing the CreateSpinBox error, frequently enough to really annoy. I particularly frequently see it when saving, but a number of different functions can trigger the error box.
To assist in diagnostics, my configuration is:
PixInsight 1.8.6
Windows 10 Professional, latest updates as of 2018-01-19
NVIDIA 1070 with drivers at 417.35
PI scratch location default (on OS disk, a Samsung Evo 850)
Images and project stored on a SSHD (2TB Seagate)
There's nothing else on the PC that could cause Qt to get confused as far as I know.
It feels like a UI/Qt issue because the underlying operations clearly still work. For instance, trying to save a file fails and pops up this error box, whereas saving the project with associated images does not (and works, so is my current workaround - only a bit of a pain with dynamic processes). Also the error talking about a spinbox which I'm guessing is the QtSpinbox class.
I have also seen that system exception - though much more rarely. I was able to trigger it after seeing the spinbox error and opening the FITS Header dialog.
I'd estimate that currently I'm getting this five or six times in my normal end-to-end processing workflow, but where it kicks off seems completely random. I've tried to come up with a reproducible scenario and failed. If there's anything I can do to enable some diagnostic/debug logging I'd be happy to provide more details.