if ($key == 48)
  {
    my %msg48;
    while(<FH>){
      chomp;
      ($key48, $val48) = split /=>/;
      $msg48{$key48} = $val48;
    }
    $msg{$key}=\%msg48;
  }
  else{
    $msg{$key} = $val;
  }


##</code><code>##


#Change:
$msg{$key}=\%msg48;
#to
$val=\%msg48;
#And lose the else around:
$msg{$key} = $val;


##</code><code>##

use Data:Dumper;

##</code><code>##

print Dumper(\%msg);

##</code><code>##

if ($key == 48)
        {
           my %msg;
           $_=<FH>;
           chomp;
           ($key48, $val48) = split /=>/;
           $msg48{$key48} = $val48;
           $val=\%msg48;
        }