AD630 Unity gain error?

Hi

I'm using AD630 (JN grade) as a +1/-1 gain amplifier to take advantage of the precise gain. However with an input of 8.06VDC (low impedance source) I'm getting output values of 8.20 and -7.48VDC in the two gain states.

I'm using AD630 connections as for the lower device in AN308 (http://www.analog.com/static/imported-files/application_notes/AN-308.pdf)

Supply voltage is +/-15 VDC. Supply voltage is clean.

I've checked all the connections carefully but I can't find the source of the gain error. Any advice greatly appreicated.

thanks

Gerry