Barebones approach that you can extrapolate into what you're looking for:

#!/usr/bin/perl -w
use strict;

open my $config, "config.cfg" or die "config.cfg: $!\n";
# Assuming the config file structure is one error per line
my %errlist = map { chomp; $_ => 1 } <$config>;
close $config;

open my $log, "logfile.txt" or die "logfile.txt: $!\n";
while (<$log>){
    chomp;
    /:([^:]+)$/;
    print "Error '$1' found on line $.\n" if exists $errlist{$1};
}
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In other words, you use the hash to store all your "valid errors", then check the actual errors against that hash. Fairly common algorithm, certainly in Perl.