Reasons for the failure of the command CALL WEB SERVICE is found by using Get Web Service Error Info command. Get Web Service Error Info (0) will return the error code, and Get Web Service Error Info (1) will return a detailed error message.
One of the common errors is a Network Fault (9913) with the detailed message 'SOAP server not reachable'. To remedy this, try to pass a SOAP call that requests smaller chuncks of data, if possible. Also, use the command SET WEB SERVICE OPTION (Web Service HTTP Timeout; TimeOutInSeconds) to increase the default timeout value. More often than not, the 'server not reachable' error is caused by the long timeout periods, so use other means to check if the server is truly unreachable.