Thread failed to start: Can't call method "createLine" on an undefined value at C:\neu3.pl line 302, <DATA> line 164.

my $mw;
my $ControlFrame;
my $ControlGraphFrame;
my $Canvas;
.
.
.
#Aufruf in MainThread:

$ControlFrame = $mw->Frame( -borderwidth=>'2',            -label=>"Kontrollelemente")->pack(-side=>'bottom',        -expand=>'1',              &n
bsp;              &n
bsp;  -fill=>'both');

$ControlGraphFrame = $ControlFrame->Frame( -borderwidth=>'2',              &n
bsp;              &n
bsp;  -background=>'white',-label=>"Graph")->pack( -side=>'top',-expand=>'1',-fill=>'both');
               
               
               
               
        
$Canvas=$ControlGraphFrame->Scrolled('Canvas',-background=>'white',-height=>$graphYSize+20,-width=>$graphXSize)->pack(-fill=>'both');    

.
.
.
#und hier der unterthread:

sub GraphThread{
    require Tk;
    Tk->import; 
    
    while (1)
    {
        if ($var==1)
        {
print "thread doing work\n";
{
   sleep(1);
   $newValue = &Measure;            &nbsp
;                     $newDraw=$graphYSize/(1<<$resolution) * $newValue;
               
 $oldDraw = $graphYSize/(1<<$resolution) * $oldValue;
               
 
               
 printf "%u - %u\n", $oldValue, $newValue;
               
 $scaleLine = $Canvas->createLine(10,10,$graphXSize,10);
               
 
               
 $count += $xShift;
               
 $oldValue = $newValue;
           }
       }
       elsif($var == 0)
       {
           print "thread waiting\n";
           sleep(1);
       }
       else
       {
           print "thread finished\n";
           return;
       }
   }
}