Running a static study in SW 2013 SP2.0, applying a large acceleration a chassis assembly.

I have a simplified, symmetrically fixed brazed chassis. I have bonded contact sets at all brazed interfaces. -Study Solves

Next I added top and front covers useing No Penetration and Bolt Connectors. - Study Solves, but much more slowly (because of bolt constraint?)

I inserted metal plates to simulate mass of installed components, using the 'bonded' contact set. - Study Solves

I am concerned that the plates are reinforcing the chassis in an unrealistic way since they are 'bonded' to my aluminum chassis.

When I take the plates and 'Treat as Remote Mass', select the face the plates rest on, and Run, the iterative calculation diverges.

Any idea why this is happening?