Please note that it is not possible to expand the duration of a transition to more than 50% of the shorter adjacent clip/colour board!
What does that mean?
If you've got a film clip and you want to have it faded out into black, you most probably inserted a colour board into your timeline of video clips. The duration of this colour board is - let's assume - 3 seconds. So your transition cannot have a longer duration than 1.5 seconds - or "1:13" (1 second plus 13 frames) in the duration window.
To get a fade-out of - let's say - 5 seconds, you must set the duration of the colour board to at least 10 seconds! Additionally your video clip itself must not be shorter than these 10 seconds either!
Maybe it's this limitation, you got stuck to...
Michael