Could it have possibly been running off the battery, while you were on the ferry?  The fridge will quickly drain a battery and the result is there won't be enough voltage to energize the igniter.  Also you need 12v to run the mother board otherwise you will end up with the scenario you describe above.  By plugging in to 120 shore power your converter will charge the 12v battery allowing the fridge to work normally. 

If you had a voltmeter when this initially happened it would be easier to troubleshoot your problem described.  Having you pod plugged into electricity for awhile will eventually charge your battery to 'fully charged' status.  If you can, grab a voltmeter or multi-tester and check voltage, fully charged 12v battery will read 12.72v, if you read this while plugged in to 120 shore power it will read 13.5v or more.  If battery checks out, try your propane once again, you should be able to hear the igniter clicking and then see the flame turn on.

I took her on a ferry.

They asked me to turn off the propane at the source.

I did.

I arrived and turned the propane back on, but the fridge just beeps with the warning light on.  And no clicking on the outside.

Before, when I ran out of propane in one tank, I heard clicking from the outside (the pilot trying to light?).  I switched to the other tank and all was well.

But now confused.

It works fine on electricity.

Thanks for any help.