if
$sql = "
CREATE TABLE TESTTABLE (id int NOT NULL auto_increment,date varchar(20) NOT NULL,prenom varchar (50) NOT NULL,email varchar(55) NOT NULL,PRIMARY KEY (id))
";
works but
$sql = "
CREATE TABLE ".$clientRef." (id int NOT NULL auto_increment,date varchar(20) NOT NULL,prenom varchar (50) NOT NULL,email varchar(55) NOT NULL,PRIMARY KEY (id))
";
doesn't, and the only thing changed is the variable, then the variable is your problem. Echo out the variable on your page until you get it to display something. When it echo's properly, then your script should work.
echo "Table Name " . $_POST['clientRef'];
// are you using post on your form? If not, try
echo "Table Name " . $_GET['clientRef'];
// or just
echo "Table Name " . $clientRef;
Hope that helps.
Cgraz