I have no idea what specific system you are using? I do not recognise the attachment types, other than the text file.
Does the analog input pin need some configuration before you can read analog (rather than digital) values from it?
eg. If it's still in digital mode or set as a "high" output, it could give that effect.
Every MCU I've ever used needs the analog inputs configuring before they can be read properly.
You also usually have to allow a short delay, a few microseconds possibly, between changing an analog channel selection and starting an A to D conversion, to allow the voltage at the input of the ADC to settle.
Edit - possibly look at the analogReference() and analogReadResolution() functions for setting up the analog input?