SOAP：参数为“SELECT sth FROM”时找不到HTTP！

I' ve a problem with Soap (I'm using it for the first time!). I'm trying to solve a problem with SOAP, used to communicate between my site and another. In SoapServer (on my site) I have a function called say_hello() that takes no argument and returns simply "hello", if I call it from a SoapClient, also with an argument, it works well. The problem appears if the argument passed is "SELECT everythingyouwanthere FROM otherthingifyouwant". I don't know why but it returns "PHP Fatal error: Uncaught SoapFault exception: [HTTP] Not Found" (404 error).

This started to happen suddenly (or, at least, I don't know the causes). On the server PrestaShop is installed.

Thanks in advance!

P.S. Sorry for my bad english!

try to pass the argument through an array.

Instead of

...
$client = new SoapClient(WSDL);
$client->say_hello("SELECT everythingyouwanthere FROM otherthingifyouwant");
...

try

...
$client = new SoapClient(WSDL);
$client->say_hello(array("parameter_name" => "SELECT everythingyouwanthere FROM otherthingifyouwant"));
...