Unproven. Please prove it, like this

# some declarations in the beginnings
  my $TAB                 =   "\t";
  my $SPACE               =   " ";
  my $oidNbrSysDescr      =   ".1.3.6.1.2.1.1.1";
  my $prefixSysDescr      =   quotemeta 'system.sysDescr.0 : DISPLAY S
+TRING- (ascii):  ';
  my $prefixSnmpWalk      =   'snmpwalk:\s*'; # no use ??



my $sysDescr  = q~
snmpwalk: No response arrived before timeout.
~;
      for ( $sysDescr ) {

         /$prefixSysDescr/ && do {
            s/$prefixSysDescr/$hostName$TAB/;
            $OutputLine = $_;
            last;
         }; # substitute some prefixes (this one works)

#         /snmpwalk:\s*/
        /$prefixSnmpWalk/
         && do {
            s/snmpwalk:\s*/$hostName$TAB/;
            $OutputLine = $_;
            last;
         }; # error messages starting with "snmpwalk:  "
            # here is the problem. All of a sudden I coudln't
            # use $prefixSnmpWalk anymore. Even quotemeta
            # failed

         $OutputLine = $OutputLine . $SPACE . $_;

      } # process output

die "$OutputLine ";
__END__

        No response arrived before timeout.
  at - line 36.
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