please help me to find the solution of this error

1- Modification of non-creatable array value attempted, subscript -1 at research.pl line 94. 

############################################
#    VARIABLES
############################################
....
# array scotching sms which was readed
my @msg2 = (); 
..........
############################################
# START EXECUTION
############################################
answer_sms();

###########################################
#     answer_sms()
###########################################

sub answer_sms
{
    #Build gsm object
    $gsm = new Device::Gsm(port=>'/dev/cuaU0');
    # read SMS of Sim card 
    @msg = $gsm->messages('SM');
    # get the number of sms in the card
    $taille = @msg;
    # read the old sms in my sim card
    proc_read_card();
    # creat array for stoching nmbr of sms in the card
    @tab=($taille);
    print "\nWAITING FOR NEW SMS.......\n";
    while(1)
    {
        my $newtime = (time+50);    
        @msg2 =$gsm->messages('SM');
        $taille2 = @msg2;
        push(@tab,$taille2);    
        if($tab[-1] != $tab[-2])
        {
        # get the number of the last sender
                # following the LINE   94#      
                my $dernier_num = $msg2[$#msg2]->sender();
                ................
              $gsm->send_sms(recipient=>$dernier_num,content=>"Error" 
+);
               .............
}
}

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when the last line is executed i get the error. Thank you in advance

In reply to Modification of non-creatable array by Anonymous Monk

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