Hi all
Just wanted to share my findings on this issue.
I have found that if you resize the Infopath Designer window so that
it only covers a quarter of the desktop, the form will then open
successfully!
You can then maximise the Infopath Window & work on the form as normal.
I have tried this on a couple of computers & it definitely allows the form to be opened successfully.
I guess it must be some sort of graphics issue or something..?
Hope this helps!