Can you provide a sample script? You're very likely doing something wrong...

the script that causes the problem :
when the string $ragsoc1 contains & in Mysql I found &

$preserve="";
while (strpos($ragsoc1,"  "))
{
 $ragsoc1=str_replace("  "," ",$ragsoc1);
 }
 // print $ragsoc1;
$ragsoc1=cleanup_text($ragsoc1,$preserve);
$ragsoc2=cleanup_text($ragsoc2,$preserve);
$indir1=cleanup_text($indir1,$preserve);
$indir2=cleanup_text($indir2,$preserve);
$cap=cleanup_text($cap,$preserve);
$citta=cleanup_text($citta,$preserve);
$prov=cleanup_text($prov,$preserve);
$paese=cleanup_text($paese,$preserve);
$telef1=cleanup_text($telef1,$preserve);
$telef2=cleanup_text($telef2,$preserve);
$fax=cleanup_text($fax,$preserve);
$mytext=cleanup_text($mytext,$preserve);
// print $ragsoc1;

// echo '$check1';

session_register("recatt_soc");

if ($recatt_soc==3)
  {
	 $a1="insert into societa (ragsoc1,ragsoc2,indir1,indir2,cap,citta,prov,paese,";
	 $b1="telef1,telef2,fax,note) values ('$ragsoc1','$ragsoc2','$indir1','$indir2',";
	 $c1="'$cap','$citta','$prov','$paese','$telef1','$telef2','$fax','$mytext')";
	 $where_cat="";
	 }
	 else
	 {
    $where_cat="where (IDSOC='$cod')";
    $a1="update societa set ragsoc1='$ragsoc1' , ragsoc2='$ragsoc2', ";
    $b1="indir1='$indir1', indir2='$indir2', cap='$cap', citta='$citta', ";
    $c1="prov='$prov',paese='$paese', telef1='$telef1', telef2='$telef2', fax='$fax', note='$mytext' ";
    $z1=$where_cat;
	 }

$query="$a1 $b1 $c1 $where_cat";


        

// echo $query;

echo "<br>\n";



$result=mysql_query($query)
 or die ("Query errata : "
          ."<li>errorno".mysql_errno()
					."<li>error=".mysql_error()
					."<li>error=".$query
					);
	session_register("recatt_soc");	
	// echo $recatt_soc;

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Can't reproduce. 

You may want to try a never version anyway, 4.0.6 or 4.1.1 ...