Hi,
Is that really ALL of the code?

When you select an analog input which you want to convert the sample and hold circuit for the ADC needs to charge the S/H capacitor. It takes a certain amount of time (called acquisition time) for this capacitor to charge up. When the the A to D conversion starts the capacitor is disconnected from the input. If the A to D conversion is started before the acquisition time has expired the conversion result will not be correct.

I'm not sure if perhaps ISIS can, based on the simulation, figure out that the acquisition time isn't long enough. I've never used ISIS (haven't been able to justify the cost) so I don't know.... From the time stamp it looks like you're doing a A to D conversion in a quite tight loop, I don't know if that's a possible problem. It think you're going to have to post more of the code.

Finally, it's not an error, it's message telling you that it has happend. It doesn't prevent the code form compiling or from running but the behaviour of the code, as written, might not be what you actually wanted.

/Henrik.