Dear Marcos,

first, thanks for the great program.  In concert with RFP 742 it makes the whole experience so lifelike I'm thinking of putting in for flight pay.

It did take me a while to figure out the trick to having everything go as planned--and I'd like to share it with my fellow simmers:

1) You must do the set-up alignment while on battery or shore power with the parking brake on.  
2) Once your ramp location is programmed in to positions 0 and 1 on the CDU(s), and the green "READY NAV" light is lit on the MSU(s), BEFORE YOU DO ANYTHING ELSE (start APU or engines, push back, etc) switch the MSU(s) to NAV.

Once in NAV, your starting position will be locked, and the INS will have a solid starting reference point. If you don't do this and move while still in ALIGN (I found) the INS gets confused and chases its own tail around the sky.

Hope this helps.  As I said, what a great program!  
Thanks

Justin