Ok. That means both $main'ora_errstr & $ora_errstr belongs to the same package. Then $main'ora_errstr = $ora_errstr doesn't make any sense.
Actually $main'ora_errstr = $ora_errstr this statement is defined in the subroutine of ora package. This package is being called by many other scripts. Some of the scripts use $ora'ora_errstr & some $main'ora_errstr. I am really confused. Please help me.