I am using USBasp to program my board with ATmega128, hardware is single side PCB by Thomas Fischl http://www.fischl.de/usbasp/
My board was working well and I decided to change some parts of the code but when I tried to read chip signature I got error (attachment) as well as when I tried to read fuse bits. I thought that maybe I have issue with CLK fuses and I applied external clock (5 V, 16.67 MHz) to the XTAL1 pin but without any success. I am confused because my board is still working as before but I cant make any change in program. Why I can not read fuse bits?