Adding some <code> ... </code> tags, it looks like this:

use strict;
use warnings;
use Win32::OLE;
use Win32::OLE::Const qw( Microsoft.PowerPoint );
use Win32::OLE::Enum;
$Win32::OLE::Warn = 3;
my $app = get_powerpoint();
$app->{Visible} = 1;
my $presentation = $app->Presentations->Open('strMgrErr.pptx');

sub get_powerpoint {
    my $app;
    eval { $app = Win32::OLE->GetActiveObject('PowerPoint.Application'
+) };
    die "$@\n" if $@;
    unless ( defined $app ) {
        $app = Win32::OLE->new( 'PowerPoint.Application', sub { $_[0]-
+>Quit } )
          or die
          sprintf( "Cannot start PowerPoint: '%s'\n", Win32::OLE->Last
+Error );
    }
    return $app;
}
[download]

When I run your code I get the same error because --of course-- I do not have the strMgrErr.pptx file on my system.

Replacing the file-name with a valid path-and-file-name, the code runs as expected.