i am working with exchange web service with our project

Fatal error: Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing WSDL: Couldn't load from '/opt/lampp/htdocs/ewsfile/email/wsdl/services.wsdl' : failed to load external entity "/opt/lampp/htdocs/ewsfile/email/wsdl/services.wsdl" in /opt/lampp/htdocs/ewsfile/email/Exchange.php:55 Stack trace: #0 /opt/lampp/htdocs/ewsfile/email/Exchange.php(55): SoapClient->SoapClient('/opt/lampp/htdo...', Array) #1 /opt/lampp/htdocs/ewsfile/email/ExchangeWebServices.php(1054): NTLMSoapClient_Exchange->__construct('/opt/lampp/htdo...', Array) #2 /opt/lampp/htdocs/ewsfile/email/ExchangeWebServices.php(478): ExchangeWebServices->initializeSoapClient() #3 /opt/lampp/htdocs/ewsfile/calender_get_item.php(48): ExchangeWebServices->FindItem(Object(EWSType_FindItemType)) #4 {main} thrown in /opt/lampp/htdocs/ewsfile/email/Exchange.php on line 55