RATAPI error on Task 1 - Latency help needed

My latency runs at around 5000 for the most part, occasionally gets to 9000 if I deliberately smash into google images and test it.

My problem is that if I set my base period to 20000 then upon opening CNC I get a real time error. The computer isn't slow or anything like that but I just wondered what this is?

Also how do I get into the latency history plot thingy, that may help me diagnose this.

Cheers all

Jools

latency-histogram

(from the command line)