Well, it nearly always helps to put a problem to this newsgroup. It helps you concentrate better!
The solution was simply, though not obvious at first.
It should not haven been "before=\nohyphens" but "top=\nohyphens".

On Jun 29, 2007, at 19:25, Hans van der Meer wrote:

I encountered some strange thing with framedtext's in trying to define one where hyphenation is suppressed. The definition is:
But then \startmyblock text \stopmyblock does not stop hyphenation.
While \startmyblock\nohyphens text \stopmyblock stops it.
Since I would like to have the myblock's all having suppressed hyphenation I am at a loss how to do it. Could it be that the \nohyphens in the "before" is overriden by something? It looks like, because setting lefthyphenmin and righthyphenmin zero at that point did not work either.
By the way it is a bit difficult to give an exact example, because hyphenation so much depends on ones linesize and font dimensions.

Hans van der Meer