As a matter of technique, you should always start your scripts with:

use strict;
use warnings;
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Doing that would have picked up that:

my $currentlog = "/perl/ass/@logfiles[$hour]";
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is better written as:

my $currentlog = "/perl/ass/$logfiles[$hour]";
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Though, admittedly, that won't solve your current problem.

To solve your current problem, I suggest you download and install the sysinternals (now Microsoft) Handle utility which will allow you to see all processes on the system which have this file open.