Hello GeraC,
I have two thoughts on this:
First at all, the NI 9403 does not seem to be fully supported by NI I2C&SPI API, at least it is not explicitly mentioned in it's package description:
Apart from that, I wonder if you already had found this posting: Using I2C or SPI communication with cRIO and NI 9403 Module [...] (it's the last posting in this thread that I am linking). Basically geashby describes the changes he/she made to use the 9403 with FPGA for SPI communication. I2C should be very similar. Is this something you could test out?
Ingo – LabVIEW 2013, 2014, 2015, 2016, 2017, 2018, NXG 2.0, 2.1, 3.0