When I run your review2.pm, I get your error. But I added a line which shows the problem. I can't figure out why it allowed you to create an Oval to begin with.?

sub paint_Info{
 
 #this shows the problem   
 my ($MW, $CW, $zoom) = @_; 
 print "\n\n@_\n\n";

    $CW->createOval( 30, 30,
                     15, 15,
                     -outline => 'red', -width => 2,
                     -tags    => ['INFO']);

    my $zfactor = ($zoom > 0) ? $zoom : -1 / $zoom;
    $CW->scale('all', 0, 0, $zfactor, $zfactor);
}
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When you print out @_, you get
MainWindow=HASH(0x7b8078) Tk::Frame=HASH(0xe2bfb0) 1
You then take $_1 and try to run Canvas methods on it. Scale will not run on a Frame, that is a Canvas method.

It just dawned on me! Your Frame is the Scrolled Frame the Canvas is in. Try getting the real canvas in your module. This fixes it! :-)

 
sub paint_Info                            #  ($MW, $Config)
{
    my ($MW, $CW, $zoom) = @_;

print "\n\n@_\n\n";

    my $canvas = $CW->Subwidget('canvas');

    $canvas->createOval( 30, 30,
                     15, 15,
                     -outline => 'red', -width => 2,
                     -tags    => ['INFO']);

    my $zfactor = ($zoom > 0) ? $zoom : -1 / $zoom;
    $canvas->scale('all', 0, 0, $zfactor, $zfactor);
}
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