Yes. The Flash MCU internal hardware go through a complex process during power up / Reset to decide whether to enter program mode or run mode. And unless you satisy the critical internal timings there, you are likely to get stuck permanently either in run or program mode, irrespective of what you want to do. Also the simple RC resets end up corrupting the boot vector and that is a even big headache.

If you search this forum for "Erik and ISP " you will end up with many pages with lotsof info on above. Also visit Erik's home pgae.

Good luck

raghu