I recently had the problem, that I was not able to program my Attiny anymore. I was a bit confused, because half a year ago, it just worked fine. Yet, as I couldn’t find any other solution (I checked the wiring about 10 times, the voltage for the attiny about 5 times and exchanged it with backup model), the only left reason seemed to be the fast mode. They say, that you can only program it with 250kHz, whereas the USBasp normally uses a bit more. However, my USBasp neither did allow setting the speed by software (firmware too old and no secondary programmer available), nor was there a slow jumper/switch.
So what’s the solution if the device costs only a few Euro and does not work at the moment anyway? Of course, the tough guys we are, we take a jumper cable, connect it with GND on the one side, and with the left hand hold it tightly onto PIN 25 while with the right hand we hit enter to execute the avrdude command!
People who are good at soldering, will manually solder GND and PIN 25 together.