Recently on a workshop, one of the participants had a recurring, but not consistent “error” message on their camera.  They had a relatively new camera and a relatively new lens and they had used them for quite a while before the workshop with no problems.  However, they were not the same brand and it really brought home the thought that when  you have that kind of an inconsistent problem, and two different brands, it is really not going to be easy to diagnose.  If both were the same brand, you could return it to the repair service of the camera with the lens and ask them to trouble shoot; but with a different brand lens, they will most likely not be able to trace the origin of the problem.  Just a thought; we know that so often some good substantial savings come in with buying a lens that is not the same brand as the camera body (and most of these are really good lenses and sometimes good buys); but keep in mind that in the future if there is a problem, it could be hard to solve.