Function (FunctionName) is not a valid method for this service

> I kept getting errors like this in soap ....

Fatal error: Uncaught SoapFault exception: [Client] Function (FunctionName) is not a valid method for this service in /file.php:118

Which was confusing me somewhat as when I did *__getFunctions* ( ) it would list out the function I was trying to use fine. It turned out that I had a soap wsdl cache enabled and that caused it to fail as once I'd switched that over in the php.ini to 0 it worked fine. In this instance I was using a local wsdl file so I didn't think to look at the caching for a long while. I'm guessing its an error cache writing/retrieval on the development machine so not typical.
Just thought I'd post this here in case any body else has this mystery, and they can check this out as a possibility.
The docs are at http://php.net/soap.wsdl-cache-enabled

soap.wsdl_cache_enabled=1

became

soap.wsdl_cache_enabled=0

I was using PHP 5.6.8 on OS X 10.8.5