That message would occur if Betfair is not responding. I recall that it was down for several hours a couple of days or so ago. See twitter.com/BetfairCS when you think it might be down, there is usually some activity there acknowledging when it is down.
Maybe Betfair was down temporarily when you experienced that error. Is it working normally for you again now? If not then please post full details of the error and the situation in which it occured. Thanks.