Does this occur when testing the analog input channels within Measurement and Automation Explorer ?
You can perform a self-calibration for your board and see if that removes a problem. If not, then I would recommend testing your board by doing the following:
Try connecting the +5V pin on your E series board to ACH0, and AIGND to ACH8, and then run the analog input test panel and read ai0 in differential mode. If it reads 5 V, then your board is functioning correctly.
Jason