Flight EGLL->EDDW.
Route from simbrief.com:
BPK7F BPK Q295 CLN UL620 TULIP UY12 SPY UN873 GRONY EEL GIBMA GIBM2P

Steps:
1) Add waypoint EGLL, then EDDW.
2) Select AutoPlan. (I wasn't happy with the suggested route, so I let simbrief create one.
3) Changed SID to BPK7F.
4) Selected BPK, then 'load airway' on P2A Waypoint Options popup. Select Q295 airway and CLN 'To Wpt'. Click load. Crash.

Trimmed log file is below (trimmed to ignore previous flight from EGKK to LFPG which went without a problem)):

Begin FPLFile 08/07/2017 15:34:31
AssignedRunway: RW17 - 
AssignedSID: RW17-TURO4S-TURON - 
FltPlan ActiveAPPR: ILS - RW22 - I22 - 
FP.FileFLtPlan executed.
ATCFltPlan set to Filed FPL
Error in btnFPLFile: System.NullReferenceException: Object reference not set to an instance of an object.
   at P2A_2016.ucFltPln.q(Object A_0, EventArgs A_1)
Application frmP2AMain ended normally 08/07/2017 15:35:06
Object of type SlimDX.DirectInput.Joystick was not disposed. Stack trace of object creation:
Object of type SlimDX.DirectInput.Joystick was not disposed. Stack trace of object creation:
Object of type SlimDX.DirectInput.Joystick was not disposed. Stack trace of object creation:
Object of type SlimDX.DirectInput.Joystick was not disposed. Stack trace of object creation:
Object of type SlimDX.DirectInput.Joystick was not disposed. Stack trace of object creation:
Object of type SlimDX.DirectInput.Joystick was not disposed. Stack trace of object creation:
Total of 6 objects still alive.

 

I just tried doing that with v 2.2.2.1 and it worked fine.  Were you using the latest version? 

An easier option is to copy your route to the clipboard, open the FP Import window (button to the right of Flight Plan) and paste it into the White area.  Then, in this case, add the Departure and Destination airports.

For the format you have here, select PFPX as the source and press import.  You'll get the full route minus the procedures, entered in one step.

Then add the SID, STAR and Approach of your choice.

Dave

Worked fine for me on the next try. Must have been a one-off.