This error normally occurs if the remote server under test (or application running on it) does not send a valid HTTP response header before send the response data to the client. Here is a sample of a SilkPerformer record log in which this error was generated :- HttpRequestHeaderToServer(#431, 221 bytes) //client makes request to server { GET http://{URL}/?SBOCMD=SBOLOGIN&AUTH_METHOD=SBO HTTP/1.1\r\n Accept:*/*\r\n Accept-Language: en-us\r\n User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT)\r\n Connection: Keep-Alive\r\n\r\n Error(#431): could not receive HTTP response header //server response header has just 2 bytes Reason: HTTP: 1000 - invalid header InvalidHeaderData(#431, 2 bytes) { \r\n } You may need to reconfigure your server or application to send appropriate response headers. Please contact Technical Support if you need further clarification on this.