I'm at a loss to explain that one I'm afraid.

 

Well, no matter.

I'm just glad I was able to work out how to actually use it, odd though it may be.
Least it does, eventually, work...lol

 

Thanks for taking the time to offer assistance.👍

Just to further add on to this issue.

I have since tested this "fix" (restarting initial flight) on my second computer that had the exact same error and the fix works exactly the same.

 

Also, another way of avoiding the error, without restarting the flight, is to change the aircraft from Airbus to an FSX standard plane (Cessna for example) and then back to the Airbus again.
This also makes FS2Crew work the second time you load the Airbus back in.