What are the values of your resistors?
These have to be carefully chosen: low enough so the circuit's output impedance towards the ADS is not too high; high enough so they don't burn due to the current. 100k sounds like a good value for the high side resistor, that way you have 1 mA to keep the ADC happy and a reasonable 100 mW dissipation at 100V.
Also the input impedance of the ADS pin is 15MΩ so you can't go too high with the resistor or it starts to affect you.