What does the error "TRANSACTION NOT ALLOWED IN CURRENT STATE 'END_OF_" mean?

TRANSACTION NOT ALLOWED IN CURRENT STATE 'END_OF_

This is one of the error which occurs when an Order is placed before market hours i.e 9:00 am.

On similar lines,

TRANSACTION NOT ALLOWED IN CURRENT STATE 'START_O

occurs when an order is placed after 4:00pm i.e market close.