Garmin 300XL GPS Approach didn't arm

Mark Hansen wrote:
During my instrument training, my CFII and I were flying into a local
non-towered airport using the Garmin GNS 430 and a GPS approach. After
passing the FAF, the unit put up a message that the approach was not
active.

I've seen that as well with a 430. More than once. And I think I've
even seen it in the PC simulator from Garmin's web site. But I
couldn't reproduce it. I think if you get well off course as the
needle sensitivity increases (just outside the FAF), it may bump you
off like that. But I never found an explanation for all of the cases
in which it happens.

Peter