After using my CO 400t for the last two weeks I've been very pleased with the GPSr itself. I've seen no issues with grabbing and holding lock, EPE has always been sub 20', normally in the teens with a minimum of 5-6 satellites at good strength. I've been walking the same trail over and over since getting the CO and the track logs for each of these are right on top of each other (within 10-20'). So far so good, until this morning.   On the walk out everything looked fine. I went off onto some new trails and starting marking waypoints until I came back to the original trail. I noticed at that point my position didn't seem to match earlier walks but I went a little further to an intersection and I could see that my position on the map was way off based on the old tracks.   When I looked at the satellite page I was surprised to see the EPE in the 70-80' range. Based on my previous tracks I would estimate my position error was off by more than 300' ! At that point I stopped for a few minutes to see if things would settle out but there was no change. I had good strong lock on 7 satellites with one directly above, 3 at ~45 degrees and 2-3 closer to the horizon. I put the GPS in demo mode several times to see if that would bring it out of its funk but I got exactly the same results. Finally I power cycled the GPS and when it came back on I had EPE of 18 and the constellation/strength readings looked identical to me. My position on the map relative to previous tracks was exactly where I thought I should have been.   These issues will drive you nuts searching for a cache.   GO$Rs