SoapFault exception: Could not connect to host

Sometimes fail to call the web service.

This problem happens all the time.

What could be the problem?

Error:
    SoapFault exception: [HTTP] Could not connect to host in 
    0 [internal function]: SoapClient->__doRequest('<?xml version="...', http://.', '', 1, 0)

Answer

The problem was solved.The problem is the cache

ini_set('soap.wsdl_cache_enabled',0);
ini_set('soap.wsdl_cache_ttl',0);