How do I unlock the app engine database when localhost runs?
So with your command to start the server which should be 
start_in_shell.sh -f -p 8xxx -a 8xxx
do include a -s flag after the -f as below: 
start_in_shell.sh -f -s -p 8xxx -a 8xxx
Sometimes some unanticipated error somewhere causes this issue. Remember to keep only one of the instances with this flag(-s) and others should be started as you do usually. 
This should make it work.
Right now I get a blank page when localhost runs, but the deployed app is fine. The logs show the "database is locked". How do I "unlock" the database for localhost?