Am I relieved that I found this topic!!!
I has a number of DNF's today. For caches I did find, while standing over the cache, my Vista HCx would report that my error is 20ft and that I am 26ft away. My HCx used to be very reliable but it has proved to be difficult since I upgraded to 2.60. WAAS was enabled. No maps loaded (using the base map).
I will try downgrading the firmware using the method described in this forum. Then I will try the ones I did not find, and maybe re-visit the ones I did to see if the accuracy is better. I will contact Garmin tech support to complain.