Hello!, I'm just begening on the flight with the B757-200
I try to get into F / P (with RouteFinder)! all others informations are entered in the FMS .. leg set, all procedures have been completed! .. ect! but after "align my IRS (10 minutes), and pass on the NAV mode I have a message Wich FMS tell me! .." "IRS enter your position." How to proceed the operation ..! please!
   (sorry, this is a simple operation, but I can not find in operating manuals Captain Sim)
thank you and good flights!

If the FMC asks you t enter the IRS Position again, just click on LSK R6 (Line Select Key    Right side, number 6) to insert it again. It sometimes has a habit of not accepting it the first time.

@Jazz777. You should, but you can do it later, especially if it doesn't accept it the first time, but if the aircraft doesn't know its own location, it can't compute the fuel usage or ETE/ETA, etc., so the PROG page will look incomplete.