$? == 256 means the child called exit(1) (256>>8 = 1). Chances are that the value (1) is not significant beyond meaning an error occurred. You'd think it would have emitted a message to STDERR identifying the error.

$ perl -le'qx{date abc}; print $?'
date: invalid date `abc'
256
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One likely cause is improper escaping of arguments. Print out $cmd, check for bad quoting, and try that same command at the prompt.

$ perl -le'qx{cat some file}; print $?'
cat: some: No such file or directory
cat: file: No such file or directory
256

$ perl -le'qx{cat "some file"}; print $?'
0
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You mentioned the child is some kind of searching utility. An error could also indicate no matches were found.

$ perl -le'qx{echo foo | grep bar}; print $?'
256

$ perl -le'qx{echo foo | grep foo}; print $?'
0
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The program's man page might identify situations where it might return an error.

Another thing to try is to replace your application by one where you can control the exit code directly. For instance when I execute (on Windows 2000) the program

use strict;
use warnings;
my $r=qx(set|perl -lwe "print <STDIN>; exit 1");
print "$?\n";
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Hi Ronald, Hi Ikegami,

thanx for helping solving the problem.

Yes another shell was running in between which did not return with "exit %errorlevel%"

really appreciated your help

Kindest regards,

Spikkie