> What is the reason for this error? I got this on
> many files from this server:

This a "Connect/receive error" (see codes below) ; but it can also be protocol
problem (such as "not enough data sent")

Any errors in hts-log.txt ?
typedef enum BackStatusCode {
  STATUSCODE_INVALID = -1,
  STATUSCODE_TIMEOUT = -2,
  STATUSCODE_SLOW = -3,
  STATUSCODE_CONNERROR = -4,
  STATUSCODE_NON_FATAL = -5,
  STATUSCODE_SSL_HANDSHAKE = -6,
  STATUSCODE_TOO_BIG = -7,
  STATUSCODE_TEST_OK = -10
} BackStatusCode;