I have this message on my car now. I bought a new cap and still doesnt fix the problem. (waste of money). Near the same time the gas cap problem happened, somethibing else has come up. My gas gauge is all over the place? when I fill up. It says its full until I would guess about a 1/4 tank. then it starts moving all over the place. Including reading full most of the time, untill the low fuel warning comes on and then I only have about 15 miles to travel befor I run out. I also have a service engine lite that seems to have come on with these problems.
Is this a bad sending unit/pump? I looked it up and they appear to be one unit. any ideas?

I read on the forum to clean the filler neck well even to the point of using fine sand paper on it. I was getting this light as well, cleaned my filler neck last Thursday night, and not had the light appear since.

As for the fuel sending unit, I'm not an expert, but I understand it is one unit, and you can access it through the black cover on the floor of your trunk.