I'm guessing you didn't use warnings and strictures (see strict and warnings) in your code. If you had, you would have received a message like 'Can't use string ("2011-01-25 10:30:50") as a HASH ref while "strict refs" in use at script name line number', which might have pointed you in the right direction. As you are new to Perl or programming, use diagnostics as well.

At the start of your program:

use warnings;
use strict;
use diagnostics;
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