Hello.

When I encounter this problem usually one of the following happens:

1. I try to run 2 MM kernels for 2 MM versions (say 1 on 10.2 and 1 on 10.4) and I use the kernel that is not "Local" for the second instance. In this case, switching to second instance to "Local" resolve the problem

2. I try to open MM notebook/ run unit test directly from workbench when I have one notebook already opened. In this case, quit all notebooks, start to run MM notebook or run test from workbench first, then run another notebook.