If there's a possibility that your file is empty, you need an extra step:

open DATA, "<$datafile" or die "$!"; 
my $dumped_hash;
{
    local $/;
    $dumped_hash = <DATA>;
}
my %somehash;
%somehash = %{ eval $dumped_hash } if $dumped_hash;
[download]

That way, %somehash is empty and you'll avoid those errors if there's nothing in the file.

Update: jcwren pointed out that I had an extra line that should have been edited out. I dare you to find it now.