use Data::Dumper

Add a semicolon:

use Data::Dumper;
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B::Deparse can help to get a little more information (Tip #6 from Basic debugging checklist):

$ perl -MO=Deparse test.pl
Global symbol "%count" requires explicit package name at test.pl line 
+11.
Global symbol "%count" requires explicit package name at test.pl line 
+14.
test.pl had compilation errors.
use Data::Dumper (my %count);
use warnings;
use strict 'refs';
open FILE, 'test.log';
while (defined($_ = <FILE>)) {
    my(@fields) = split(' ', $_, 0);
    'count'->{$fields[1]}++;
}
print Dumper(\(%{'count'}));
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Here it shows that my %count looks like it's being passed to Data::Dumper.