Thanks for your reply John but I tried to set up the ERX for 2 hours, I'm pretty sure I have tried everything.
At the end I looked at the zaxnet info and I discovered that there was no zaxnet version written on "about nomad " screen
The problem seems to come from the nomad Zaxnet, that's what Zaxcom told as well .
For the moment the only solution I have is to send the device back to Zaxcom and that would be very costly for me , that why I ask if someone as ever experienced the same issue and managed to resolved it