I upgraded to version 6.7.19.0 last night and since then, my "Preferences" window is invisible.

That is, I click on Preferences and the window appears to open, but it is not visible. If I mouse over the Wealth-Lab icon on my task bar, it shows an open preferences window, but is not on the screen, and it is not hidden under any other windows. Everything else seems to work ok.

I was wondering if anyone else is having this problem, or is it unique to my system? I have tried re-booting, but have not done a complete deletion and re-install yet.

Whenever you have an issue, start right from the Errors section. Chances are it's already reflected there:

Wealth-Lab or one of its windows is not displayed

I had the same problem... I couldn't see the wealth-lab preferences...

I followed the instructions and now is solved.

I have nothing else to add to my reply #2 above which you probably have overlooked. Typical questions and problems are documented in the FAQ and Errors section.

QUOTE:
I have tried re-booting, but have not done a complete deletion and re-install yet.

On a related note. After all these years it's an unsolved mystery to me as to why folks try a "complete deletion and re-install" without looking in the FAQ first.