GPIB timeout during ReadByteArray

Hey all, 

Trying to set up a new testing set up for LIV measurements. I have a Keithley 2400 SMU and a DMM 6500. 

Communicating with a GPIB-USB-HS (but have also tried the +).

It can write commands fine, but seems to send the ReadByteArray twice, like in this post (Solved: .Net GPI Device ReadByteArray method beeing called twice - NI Community) I'm not sure how this person actually fixed the problem, though. 

I've been using the NI 4882 dll (version 13.0.40.159 and 13.0.45.161), the net framework for the VB code is 4.8.1. 

I've read all the posts I can find on this topic, I've tried to add the termination character using the NI MAX settings, but get the same timeout error. 

I've increased the I/O timeout to long times >100s and still the same problem. 

Any help would be appreciated, 

Maria