AT&T Microcell will not activate.  3G light flashes green.  Step four fails.  Error.

This error can happen even though you have had a Microcell for years and only unplugged it for a few minutes.  When you plug it back in, it initiated a check of its position against your address to make sure you didn't move it somewhere new to prevent emergency response being sent to a no longer current address.

"But I didn't move it at all!"  "I only moved it upstairs."  "It's in the same place it has been working for years!"  See below.

AT&T has installed an address/GPS coordinates database used to check the GPS coordinates reported by your Microcell during the activation process against the address you input where it is installed.  Although the database must only report the address and the coordinates to be within five miles of each other, some locations are out of agreement by more than that, reportedly mostly at rural addresses which was my case.  You will get a steady green Power light, steady green Ethernet light, a steady green GPS satellite light (in a few minutes), the computer light will be out if you have connected your router directly to the Microcell, and the 3G light will flash slowly... forever.  When you monitor the progress of your activation on the AT&T web site, the first three steps will complete normally and step four will fail.

When this happens, you should call AT&T Microcell support at 800-331-0500 and let them go through their trouble shooting procedures with you.  If the above is the cause of your trouble, the CSR will eventually tell you that their system reports that there is a disagreement between the GPS coordinates and the Microcell's address you put in.  The CSR will fill out a ticket to have the disagreement corrected manually; that is, these fixers will have to tell AT&T's system that such and such coordinates really are at your address, not somewhere over five miles away.  (In my case the ticket was sent to the wrong people the first time, delaying the fix.)

Some people in Tier Two support know how to make the correction themselves, but they don't want to talk to customers, so unless you want to move yourself a little further down the road to your stroke insisting on talking to them, just ask what the ticket shows for the completion date and time and go make your calls from somewhere else until then.  In my case, that was three days later.

A day after the promised date I noticed mine was working, but because of a quirk in my phone's display, it might have been earlier.  In the past, my phone continually displayed "AT&T Microcell" or "AT&T Micro" at the top of the screen when I was home.  This year (I connect my Microcell seasonally) on the same phone that message was only displayed for about five seconds after the screen first lit up (Samsung Galaxy S4), then disappeared to make room for additional icons, like message waiting or email received.  That bumped the "AT&T Microcell" message to the bottom of a screen that is not displayed until you swipe one finger down from the top of the screen.  Since that screen is not displayed until you perform the swipe, the Microcell might have been working on the promised day.  However, an AT&T employee called to see if my Microcell was working about an hour after I noticed it in service, so I doubt it.

Nickel knowledge: If you would like to know your precise latitude/longitude coordinates without a GPS or figuring out how to get them out of your phone, here is an easy way.  Open Google maps on a real computer.  Search for your address.  Note that Google does know where your address is, even though AT&T does not.  Click "Satellite" in the upper right to switch from a street map to a satellite image.  Zoom in and find the exact part of the house/street in front of it for which you want the coordinates and right click that spot.  Choose What Is Here?  Look at the box where you entered your address earlier.  It will now contain your coordinates in degrees to the millionth of a degree.  Note that Google uses only degrees and fractions of a degree, not Minutes (1/60 of a degree) or Seconds (1/60 of a minute), nor do they use E or W longitude, preferring to use positive numbers for north latitude and west longitude and negative numbers for south latitude and east longitude.

How precise is a millionth of a degree of latitude?  One nautical mile is 6076 feet, so 60nm is 60 x 6076 = 364,560 feet.  Move the decimal six places to the left and we get 0.364560 feet for one millionth of a degree, or about four inches!  Since all longitude lines converge at the north and south poles, they are only 60nm apart per degree of longitude at the equator, so a millionth of a degree of longitude can range from four inches down to a zillionth of an inch.  Precise!