A/D with ref on AIN2 & AIN...

[Ttelmah]

I'd be suspicious that your main problem may be a compiler 'glitch'. 3.182, is pretty old. You need to run the code in a simulator, and see if the value in the ADC configuration register, is what is expected.
However the comments about the accuracy remain. You need _both_ sources to be able to maintain a good supply, with a wide range of loads. One zener, is not going to do the job. You either need two voltage references, or a single reference, with a divider, and buffer amplifiers.
The second question also remains about the analog inputs. If any of them go below the Vref- (by more than a diode drop), current will flow, pulling the reference pin down. Remember that this applies to the other unused analog inputs as well in the mode you have selected.
The only way to get a proper 10bit accuracy from a signal like this, is to amplify it before feeding the ADC...

Best Wishes

[abx]

I've checked the ADC configuration registers and all seems ok.
I've also ordered the release for my compiler...
Note that all work well on a PIC16F877A. But there is not enough memory for my complete program.