Would like to ressurect this one.
I am having the same issue, which is very inconsistent.
Here is my hook up. (newes beta drivers)
1. Samsung monitor into DVI of R9 280X (via dvi to hdmi adapter)
2. Sony TV into AVR (via hdmi) - > into Display port of R9 280X via HDMI to DP adapter.
When I try to extend my display to Sony TV... sometimes it works fine (esp if the TV was already running and i boot up the PC after).
But sometimes i get the error saving configuration, like the OP. After that error second display (sony) will dissapear all together and i have re-detect it via device manager. And then it will let me extend / duplicate.
This is a very sporadic issue... i have not been able to find any particular pattern.