Resistor in my amp design caught fire, is my design incorrect?
Have you calculated the power dissipation for R28 and R29?

The schematic is a bit fuzzy, but I take R28 to be 100K and R29 to be 470K.  Those are large values, but you have the supply voltage given as 366V, which makes the total power rather high despite the high resistance.

I find 0.2 Watt for R29, and less than 0.1 Watt for R28.  These are worst case (Q3 completely conducting,) but I think you need resistors rated for higher power.  Like, 1 Watt.



Now that the values have been corrected, things change drastically.  

R28 will dissipate 1.3Watt worst case.
R29 will dissipate 0.06W worst case.

If R28 fails to a lower resistance, then the power through R29 goes up, which would destroy it as well.