Remove the 'Content =>' portion. See perldoc lwpcook and the second example in the POST section.

In the future, it would be helpful to see the exact error message you've received.

Update: Since we can't tell what's in %hiddenhash, the best I can do is to speculate that there's an extra value in there that the server doesn't like. You might use the debugger or Data::Dumper to print the hash to verify that it contains exactly and only what you think it should contain: 

use Data::Dumper;
print STDERR Dumper(\%hiddenhash);

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In reply to Re: Post with parameters using hash by chromatic
in thread Post with parameters using hash by Anonymous Monk

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