Using Data::Dumper, do this:

sub MakeDateTime {
  my $self = shift;
  my ($Year, $Month, $Day, $Hour, $Minute, $Second, $MilliSecond) = @_

  print Dumper \@_;
  
  ...
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It looks like there might be something unexpected at the front of the params array that may be confusing DateTime/Params::Validate, per this line in the error:

DateTime::new('undef', 'year', 2015, 'month', 08, 'day', 24, 'hour', 1
+7, ...) called at MonitorClass.pm line 80
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DateTime may fail with your error if it can't figure out the locale, but your time_zone param is set properly so I don't see that being the issue. Also, please let us know which version of DateTime you're using.

-stevieb