The South African Airport Authorities have updated the Hand luggage restrictions as of 1 February 2015. Here is a press release;

As of the beginning of February 2015, Airports Company South Africa (ACSA) has implemented tighter hand luggage restrictions.

Economy class passengers entering a commercial aircraft are now restricted to:

1 bag + 1 slim-line laptop bag.
No bag should exceed these dimensions: 56cm + 36cm + 23cm = total dimension of 115cm including handles and wheels.
Weight limit per bag: 7kg.

Business Class passengers are allowed an additional carry on bag.

Any hand luggage which exceeds these stipulations will have to be checked-in. Passenger will be referred back to the check in counters to check in the non-compliant hand baggage as hold luggage. Airlines won’t accept responsibility for any delays or missed flights caused if your had luggage doesn’t conform to these measurements. Individual airlines may have exceptions, although one of their representatives will have to clear this with airport security. Approval for a greater allowance can only be done by the airline on the passenger’s behalf.