Note that inline is default. You don't need to list it. Also, the filename shouldn't be exactly like the path. Here, I used "differences.txt". Here's what I came up with:

#!/usr/bin/perl

use strict;
use warnings;
use MIME::Lite;

my $msg = MIME::Lite->new(
    From    => 'some1@somewhere',
    To      => 'some1@somewhere',
    Cc      => 'some2@somewhere,some3@somewhere,some4@somewhere,some5@
+somewhere',
    Subject => "Fetch issues as on 'dateFile'",
    Type    => 'multipart/mixed',
   );
$msg->attach(
    Type     => 'TEXT',
    Data     => "Hi,Please find attachement for Fetch issues seen in c
+ategories  as on 'dateFile'",
);
$msg->attach(
    Type     => 'text/plain',
    Path     => '/root/Desktop/exceptions_reasons.txt',
    Filename => 'differences.txt',
);
$msg->send;
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