So if I understand you right you only fail to flash new chips. Well, new chips run on internal oscillator at 8 MHz with ckdiv 8 by default --> the timing does not fit at all. However at least they can be flashed. If you use the IDE to flash them then the IDE will flash the standard fuse setup for running with external crystal. If you do not have this then the result will be that the target will have no clock. No clock implies no possibility to do anything with the chip. Either you set it up with a crystal or you will be stuck.
So does your setup include an external crystal or resonator? Or did you change the IDE fuse setup to 8 Mhz, ckdiv 1?