Try with older drivers(13.12).
This. very much this. If the config from the ultracoin site launches on your card, you will not get HW errors unless you're using drivers beyond 13.12.
Best GPU for the money for mining YAC is still the R7 240 4GB sapphire card. $70 card nets 365 -370 Hash/sec, and works perfectly fine with 1x risers.
As for how much one is making in a day, right now is _not_ a good time to determine that - the difficulty is still adjusting to the new network hashrate and hasn't hit its equilibrium value yet - look for it to hit ~90-100.
I think I need do full clean installation after change from R9 280x to R7 240 4Gb (sapphire)
My system is win 7 64
Drivers need change to 13.12 this is clear.
Some more questions
Yacminer and ultracoinminer (latest versions of course):
Do these need SDK also? And if need, what version exactly.
(previoussly in R9 280x rigs for N11 coins I have used SDK 2.8 with 3.7.2 "Kalroth's" CGminer )
If there is small rig's with 4x R7 240 4Gb what is recommended system memory. 8G still enough for YAC?
Are there any problems with x1 risers and how much these loose hashing power.
(With Nvidia 750Ti's I have big problems with 1x risers)