Plug-in FP & FV batteries show "Not Compatible

I have both a SONY digital tape video camera (DCR HC32) and an all digital SD card Sony video camera (HDR PJ260). Each take the plug-in style battery packs which are almost identical in the way they plug into the camera body.
Recently two of my fully recharged batteries when installed on the camera showed an error message of 04.00 with the message this battery is incompatible with this camera.
These are tried and true batteries used for a couple of years so the message had to be incorrect.
I have found the solution.
Take the battery back off your camera. Look carefully at where the battery plugs into. You will find three copper fins that accept the slots of the battery pack.
These fins get dirty. They may not look like they are but after carefully scratching all the metal surfaces with a teeny tiny jewelers screwdriver, the battery was reinserted and the problem disappeared.