Star Alliance - South African Airways won't clear flight

I have been trying to book via United a flight that will take me from IAD - FRA on UA, FRA to JNB on LH, and JNB to DUR on SAA. United keeps telling me that SAA won't clear my flights from JNB - DUR and back. This is so frustrating. Any idea why SAA won't clear the flight, there are plenty of seats.

1. What did SAA say when you called to ask?

2. SAA has 72 hours to confirm under IATA convention and some carriers take that time. Has it been 72 hours?

Any idea why SAA won't clear the flight, there are plenty of seats.

Presume you are wanting SAA to add an extra award seat?
Why would they?

I have been trying to book via United a flight that will take me from IAD - FRA on UA, FRA to JNB on LH, and JNB to DUR on SAA. United keeps telling me that SAA won't clear my flights from JNB - DUR and back. This is so frustrating. Any idea why SAA won't clear the flight, there are plenty of seats.

Is this an award booking? Then your flight will not clear. Unless SA opens new award seats for the general public which they might or might not do you will be out of luck. Just buy a cheap revenue ticket for that segment. Or take the bus, its a nice journey.