Hi,
Ah, so you had it configured for external VRef but didn't use that - that would explain it. Strange it didn't help when you reconfigured...

Have you verified the pot and connections, does the voltage at RA1 actually change when you sweep the wiper of the pot? Don't you have ANY other pot with lower resistance you can try with? If not just try with a simple resisotr divider.

Since the forum messes up displaying binary numbers I'm going to write them in decimal instead.
If you set the lower four bits to 0100 you'll get 3 analog inputs on AN0, AN1 & AN3 with Vdd/Vss as VRef.