Inverter not accepting A/C power-advice?

Is this your inverter? It has some impressive specs, like a 8400 watt surge capacity, no problem starting a piggy AC unit with that :)

http://dimensions.sensata.com/product-inverter/2000w-12vdc-quasi-sine-inverter-charger

Since you have the "R" for remote diag panel, what is the panel showing, can you post us a picture of the diag panel?

No adaptor on 50 amp plug. Just tried the shore power test; did not solve problem. Don't have a voltmeter. If transfer switch is stuck in invert position, how to fix?

I'm not familiar with this particular unit. Assuming it's an IC with a transfer switch, it sounds like the xfer switch is stuck in the invert position.

As mentioned, test incoming and outgoing with a vom. As an emergency measure, if you have a spare charger, put that on the batteries and continue running on the inverter.

You need to test the shore power connection.
You could try shutting off all circuit breakers in the rig. Then shut off the shore power supply breaker. When shutting off, apply light pressure toward off.
Turn on shore power breaker, then turn on main breaker in the rig. Next turn on each branch breaker one at a time.
You didn't say whether you are using any type of adapter on the shore power cord.
Do you have a voltmeter?

Nothing works when you plug into outlets. Reefer, A/C, etc. are working. It is things like clocks, microwave, television that are not working. If inverter is turned on, everything works off of battery power. If inverter is turned off, outlets don't work. Batteries are going dead, charger is not working.

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A 50 amp shore power has two 120 volt legs of power.
Some of the loads with in the rig is powered off one leg and other loads are powered off the other 120 volt leg.
You are using the 50 amp plugged directly into a 50 amp receptacle, is this correct?
What other 120 volt devices are not working? Does water heater have a 120 volt element? Does the refer work on 120 volt? AC units?

Wow, was working fine today-then this happened. It is a Dimensions Unlimited WIN-12x20B3RT.

Sounds like the inverter has gone belly up, what make and model is it?

Hooked up to 50 amp...what do you mean by "one leg open"?

What kind of shore power are you connected to? Is your rig 30 or 50 amp?
Are you using an adapter of any kind?
It is possible if 50 amp rig one leg that the inverter is on is open.