My original target fuse setting:
Ext. Crystal/Resonator High Freq.; Start-up time: 16K CK+64ms (CKSEL=1111 SUT=111)
I then switch to:
Ext. RC Osc
Int. RC Osc
as I'd intended.
Now I get the "Check the ISP Freq" error. :( How do I recover this device? I seem to be completely unable to do anything further. :(