ainser64 and potentiometer >=10k

Hi !!!

Why can not I use potentiometers over 10K?

I noticed that the 50k (linear B) potentiometers connected on the ainser64 board do not send CC = 63 when it is midway (5V / 2 = 2.5V), but sends CC = 63 when it is just over halfway down (2.90 V) at the entrance of 4051.

Sorry, my english.

 

Tks, Marco