We have three Arduino AT Mega 168 here and tried to connect 4 lightsensors at the 4 analog ports. The result was that all sensors were working correctly except analog #2, the light sensor on port #2 returns very confusing values when others return 1023 it returns 800, wenn we darken the room all returns something like 50 , analog #2 returns 400. We tested different sensors to ensure working hardware, we changed resistors and it seems that 3 of 3 arduinos deliver wrong values on analog #2. Is that possible or are there any other possible sources of error?
Strange. Did you get problems when there was only one sensor connected? Or did it only happen on pin 2 when there were also sensors on other pins? How did you have the light sensors wired?
if your sensor #2 returns the same "incorrect" value on different Arduino boards, then it is not the Arduino hardware itself. Photocells often look a like but have different light/dark values and ranges. What happens if you measure the resistor and the photocell values with an ohmmeter?