Hello fellow PoP players,
First time I'm checking back since late September 2011. Nice to see that PoP is still the premier mod for Warband
As for the error, I checked and it is indeed a bug that at most could prevent one of the dialog menu response options to appear. It will not affect any King's weapons though.
Basically, if you captured a noble you may get him to re-join you but there is a (try_end), that is without a (try_begin). The menu option that is supposed to appear if you captured a noble is:
Very well friend, I will accept your Oath of Fealty.
There should be no (try_end) in that pre-requisite segment of that dialog response option.
If you have a save game and can test this situation again, I can send you a fixed version for this warning issue and you can test to verify that it is fixed. An extra (try_end), has likely no real effect in this case except for generating that warning message.
WB 1.150 should be out soon and hopefully PoP will still be compatible with no bugs after 1.150 is installed. We might want to port PoP to 1.150 if there are new features that improve the game. Also we probably will need to port it if there are incompatibilities between PoP for 1.143 and WB 1.150.
Edit: As for the number of kingdoms required for you to be able to demand a weapon of a King: The King's kingdom must have 5 or fewer centers. If it has 6 centers or higher, you will never be able to demand a Royal Weapon.