php,soap_SOAP-ERROR: Parsing WSDL: Couldn't load from，php,soap

SOAP-ERROR: Parsing WSDL: Couldn't load from

php iis SOAP
程序正常，但是动不动就会变这个错。
SOAP-ERROR: Parsing WSDL: Couldn't load from
重启iis就好，一段时间后又会，是主要什么原因。求解决