R. Aranda S. wrote on Dec 14^th, 2011 at 3:04am:

CoolP; closed FSX, opened it again and joined the default flight with the Trike Ultralight over Friday Harbor and Fair Weather, etc. Loaded my 767 flight and now it's flyable. It's just to open the flight though another one I guess. Morten thank you very much.

Glad it solved your problem!

In fact you only have to open the fsx Default flight for a short moment, that is until it has launched fully (but you don't have to actually fly!). Then from here go directly back to set up your aimed new 767 flight through Free Flight.
Actually, I also remember PSS's 747-200 having that procedure to it - not just as an option - but as part of a obligatory standard procedure, before each and every time you were going to load their 747!
I guess, it properly was the PSS support department that had introduced that rule...getting tired of dealing with all sorts of black magic..!  :)