gr4eme,
The left side of R84 should go to OUTA. The right side of R84 should go to INB-.
Break the connection from OUTA to R84.
As a side note, the abs max for the AD8599 is +/-18V. If you have a small spike on the +18V,
all bets are off and we will not accept returns. You may affect the long term reliability or
cause a catastrophic failure.
It looks like you are building the classic four resistor difference amp. All four resistors have
to be tight tolerance to get decent DC CMRR. The caps have to be matched also (expensive!)
to get decent AC CMRR. See:
http://www.analog.com/library/analogdialogue/archives/48-02/diff_amp.html
You may want to consider the AD8271 or AD8274.
Harry