I use a Keithley 2400 over GPIB for photovoltaic J-V measurements and I've not used the drivers. I use the basic VISA functions and send the commands myself (the manual is extremely well documented with all the commands you need).
Attached please find an example vi with 3 subvi (4th file in following post). These set up a linear voltage sweep and a buffer of user defined size (number of points in sweep). It then initiates the sweep measuring voltage and current. The wait vi probes the SRQ bit of a registry (also documented in the manual) to determine when the 2400 buffer is full. Then I read the values; using the buffer prevents reading an incomplete data set. NOTE: The source2 ttl output in my code is simply for a mechanical shutter in my system.
I'm not suggesting you replace your code with mine, I just wanted to show you something that works. In regards to the -110 error. I've often seen this when sending a command that is out of the specified range OR a command is formatted improperly (such as a missing/etra spaces/comma). In regards to the range issue.
For the voltage source, the keithley 2400 has two voltage ranges (+/- 2V and +/-20V) if you want to exceed the 2V value (i can't see that actual voltage value in your picture), you MUST first specify that you are using the 20V range. Note that this higher voltage range corresponds to a lower current range (see manual). Another point is that the "current protection" MUST be LARGER than the "current range" (a common oversight).
