R6260 can't ping my Nighthawk aircard

I just replaced my failing R6080 (AC1000) with an R6260 (AC1600).

I wasn't surprised that the setup was all but identical and everything went smoothly and worked the first time except one thing:

I have a Nighthawk aircard (AT&T Mobile) in my van that I use for various purposes but in particular for syncing files between my laptop in the van and my principle desktop at home.  This worked and has always worked with the old R6080.

But it will not with the new R6260, no matter what I do.  In particular, I can't even ping the aircard from the R6260 or vice-versa, though both can ping every public internet site I can think of without a hitch.  The laptop can get the IP address of the home domain (mepelan.ham-radio-op.net) via the aircard but ping, whether to the URL or to the IP, still fails.

So is there something that must be set up differently on the R6260?

Thanks.