I have the same card, now at 2.5 with I=16, HW errors at i-18.
Just to confirm I am talking about x13 algo
Yes, x13.
Hmm. Ok. May it depends from other hardware:
I have 2 videocards o my PC: 5770(working + games) and R9 280(mining) and 32Gb RAM. Maybe this mod requires more system memory. How much do you have? Or maybe it's just hardware luck variance. My vga bios version: 015.041.000.000.000000(113-AD47800-101)