THE BOTTOM LINE
Considering all the possible combinations among Windows operating systems, Arduino IDEs and libraries, it is not difficult to get in trouble. What follows has been tested for several weeks.
1) Windows XP + IDE 1.0.6 + Arduino UNO work fine with sketches both not incorporating or incorporating the WIRE library.
2) Windows XP + IDE 1.6.0 to IDE 1.6.8 + Arduino UNO work fine if the sketch does not use the WIRE library. Of course the sketches developed for the ZERO cannot work with the UNO as the Processor is different.
3) Windows XP + IDE 1.6.0 to IDE 1.6.8 + Arduino ZERO work fine if the WIRE library is not used. Sketches with the WIRE library do not compile. E.g. Sketch_Universal_Translator_8 works, Sketch_Universal_Translator_8_I2C does not work.
AMENDED 16/5/2016: IDEs 1.6.6 and later have been modified & improved, therefore Windows XP + IDE 1.6.6 to IDE 1.6.8 + Arduino ZERO work fine with or without the WIRE library.
4) Windows 7 + IDE 1.6.0 to IDE 1.6.8 + Arduino ZERO work fine with both sketches, e.g. with or without the WIRE library.
Enclosed are PC shots of system operation with Picolog 1012 DA. Remember to set the AREF to 2.5V in the sketches. Also consider that the Optocoupler output transistors are losing 200 mV approx., so that the PWM peak is at 2.3V and this loss introduces an error that must be corrected in Picolog (table or equation or file). Another way to overcome this problem is to set AREF @ 2V, while leaving the Opto feed @ 2.5V, restricting the dynamic range and correcting the excess again in Picolog. I do not advise to set the Regulator @ 2.7 V, as this might damage the 1012 inputs in the long run.
Since the 1012 does not have a +5V output as the DrDAQ, a simple USB "cheater" can be used to "steal" the 5V to feed the Optocouplers supply from the PC USB bus.
Once these issues are addressed, calibration stability is excellent.