Conductance-Atomic Force Microscopy (C-AFM) was used to study CdSe nanocrystal-solids. Measurements taken under positive tip bias were found to be repetitive, the IV curves exhibiting a staircase-like structure. In contrast, under negative tip bias the current was observed to decay with time. Furthermore, the application of negative tip bias causes a reduction of the otherwise stable positive bias conductivity. This alteration was found to be restricted to a radius of several hundred nanometers around the point of application and to slowly fade with time. Illumination or an application of a large positive tip bias were found to shorten the recovery time. This phenomenon was not observed for identical macroscopic contacts the IV curves for which were found to be linear. We interpret these results as being due to charging of the surface states of the nanocrystals in the proximity of the tip-sample contact area.