The RX have been a very popular mod for some reason that escape me as I've never seen such a problematic mod, many, and I mean MANY people reports issues with them. The connector is usually the biggest flaw and any tank that's got a slightly longer tip ends up crushing the pin/510 connector and you end up with these messages.
Of course, there's a chance that your tank might have a fault, so try to test it with another mod, but odds are, the pin is damaged and a bad contact is happening.
Some people fix this with prying the pin back up a bit, others need to replace it, others open the mode and find that the connector connection inside was broken and re-soldered it. Some simply unscrew the tank just a bit, and you can put a padding (non conductive washer/separator) between the tank and mod to prevent this.
Basically, the RX cannot handle any tank with a longer 510 tip than the standard, and if I remember, your tank is one of those.
Note that I've seen other issues such as some batteries not fitting right (not tight enough) causing other issues due to the bad contact with them (giving you error messages).