PHP Fatal error: Uncaught SoapFault exception: [Client] looks like we got no XML document-Collection of common programming errors

I have written simple api in php to connect with magento. This api works fine if I pass simple parameter like string,int to it.But if I am going to add array or some complex data type I got above exception.

I think it is problem with wsdl file. I got wsdl file on site http://www.magentocommerce.com/boards/viewthread/43818/ What should I add to wsdl file so that it will allow me to pass complex data type as a parameter. I need to write one function that will accept array(key=>value) pair and will return simple string message.I have seen wsdl of catalog for study but I don’t understand what should I put in complex tag. Please help me!!!