This is because your position is assigned to deferent Personnel area and your trying to asign this position to person who is in deferent Personnel area.
What you can do is either adding the correct personnel area in PA Side or go to T. code PP01 and and select account assignment and change the Personnel area.
Then you won't get this information error.
How about if I need to change the PA for the position that is already assigned to a Personnel Number? I changed the PA at the position level, it is different then the current PA for the position. Then I ran PA40 Action Update EE and I am getting the above error. Is this the wrong process?
If you changed the PA in position level ( I hope your doing this in account assignment info type in OM) before doing the PA40 action then you won't get this error messege.
Now itself you getting warning message. If you press ender key two times then system will allow you to save it.