I had the same problem today, was OK yesterday and I have noticed that the way geocaching.com displays caches with google maps has changed since yesterday, so I put it down to something that they changed on the website, as I haven't changed anything with my Garmin or PC.
Edit: I've just read on the Geochaching.com thread that others are having the same problems and Groundspeak are looking into it. Hopefully should be sorted out soon.