I tried to disable the connect and the disconnect in the sub before I looked for help here but that didnt do the job.

Looking again at sub UpdateDb, I see you have the same problem with the $Sth variable: you call prepare and finish on it, so, when the subroutine returns, the call to $Sth->fetchrow_array in the while loop is no longer valid. Here’s a suggested rewrite of the subroutine (untested):

# Update the selected Database record

sub UpdateDb
{
    my ($dbh, $upd_query) = @_;             # $dbh is already connecte
+d

    my $sth = $dbh->prepare($upd_query);    # create $sth as a local, 
+lexically-scoped variable unrelated to the global $Sth
    $sth->execute() or $ErrNum = '3007';
    $ErrMess = $DBI::errstr;
    $sth->finish();
    print "HIER $ErrMess<br>"
}
[download]

You would call it like this: UpdateDb($Dbh, $UpdQuery);

This is still far from ideal, as $ErrNum and $ErrMess are still being used as (effectively) global variables¹. But localising $sth, by declaring it within the scope of the UpdateDb subroutine, will allow the call to $Sth->fetchrow_array in the while loop condition to work correctly.

¹Strictly speaking, the only true global variables in Perl are the built-ins, such as $| and $/. Variables either declared with our or used without being declared (in the absence of use strict 'vars';) are package globals. Variables declared with my are lexicals, meaning they have lexical scope. But when I talk of “(effectively) global variables” I’m referring to the “action at a distance” problem which arises when a variable is used across so wide a scope that it becomes difficult to manage.

Hope that helps,