PXI 6030e Voltage measurement

Hello All,
I have a PXI 6030E DAQ with a SCB-68 connector board.  I am setting up a simple voltage divider and connecting my Vout to pin 68 on the SCB-68.  My ground is going to pin 67.  My Vin is 5 V DC.  I used DAQ assistant to automatically generate code to read the voltage and put it in a while loop.  My R1 is a device (Copper Interdigitated Electrodes coated with Dow Corning Silicone), and my R2 is 100 Mohm resistor.  I am using an OP Amp as an isolator between the impedance on my DAQ and my voltage divider.  Unfortunately, when I run this program it will not reach a steady value or progrssively drop the voltage.  Is there something I am missing here as to why it will not allow me to get the reading I want?

Thank you!  I actually found it last night 5 minutes after I wrote the message.  I constructed the Wheatstone bridge and used a differential reading from the 2 nodes connecting each leg.  Unfortunately I received a reading that is about 10 % higher than what I calculated.  When I do a reading with respect to ground (RSE) and probe both sides of the bridge separately (with a single channel, not simultaneaously) I simply subtract the reading I receive from each side and obtain the correct value.  Ideally when using the differential method in DAQ Assistant  it is suppose to give me the right reading, but why is this giving me a different value when DAQ assistant is configured to take a differential reading.  My program is exactly like the example provided by NI.  Except I am adding the values from each signal and outputing them to a numeric indicator vi. All suggestions are welcomed!
Thank you.

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    '˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

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