......
#gui();   # works
#       below fails 
my $gui_thr = threads->create( \&gui );
my $res1 = $gui_thr->join();
...
sub gui {

# mw contains frames 1,2 and 3 top to bottom
    $mw = MainWindow->new( -background=>"$stock_bg");
    $mw->resizable( 0, 0 );


##</code><code>##

8763dbc is not a hash at /usr/lib/perl5/Tk/MainWindow.pm line 55.
Aborted