Function return

["Dan Shirah" <mrsquash2@xxxxxxxxx>]

TGIF!!

I have an insert statement that checks to see if a condition is met.  If it
is, then it adds that value to the insert statement.  However, when I try to
run it I get the error: Can't use function return value in write context

Below is a sample of what I am using which gives me the error(The error
occurs while trying to insert the "due_date")

$insert2 = "INSERT INTO misc_service_payment_request SET";
   if(empty($_POST['max_id'])) {
      $insert2.=" id = scope_identity(),";
      } else {
      $insert2.=" id = '$max_id',";
      }
   if(!empty(trim('$due_date'))
   $insert2.=", due_date='$due_date'";
mssql_query($insert2) or die ("Query failed: <br
/>".mssql_get_last_message());

Any ideas?