RE: dsPIC33FJ128MC804 Voltage Reference problem
Did you fix this yet? It seems what you are trying to do is eminently reasonable. After all, the Comparator Voltage Reference is essentially a low-resolution, 4-bit DAC. Should work.
I have ruled out hardware as a source because it works some of the time. The only two things I can think of are an incorrect configuration of the CVRCON register (unlikely), or an out-of-spec voltage value for the VREF+ ADC input. The minimum is 2.7V. What voltage did you set the CVR to produce?