Problem With Current Assets

[Les]

I have a set my chart for accounts under Current Assets: Cash, then 
various banks etc.  Today, I decided to add a sub account to Cash: 
Banks.  In attempting to place the various banks under "Banks", one of 
my accounts got accidentally placed under another bank and I cannot 
figure out how to undo it.  When I try to change the parent account I 
get a message "you must choose a valid parent account".

I can't figure out how to correct this.  Probably just brain dead. I 
have changed structures before without any problem.

System is LInux Mint 18.2 and GC 2.6.17.

Any help, greatly appreciated.


Les