NE was an obsolate alias for ne, which is removed completely from newer perls. You should just use ne if you mean string comparison, and != for numbers; in this example either are the same.

Perldoc perl570delta documents this change:

Incompatible Changes

• The long deprecated uppercase aliases for the string comparison operators (EQ, NE, LT, LE, GE, GT) have now been removed.

(Note also stdout, which is an alias for STDOUT, but that is still supported. And the same for STDIN, STDERR)