Mike Rife
Ansys Employee

Hi Diane

An "Usual Suspect" would be stiffness terms, especially contact stiffness, that are being rounded off.  On 'small' models that use MKS the stiffness' can get to be => 1E16 which can/will be rounded in double precision math.  When changing unit systems down to match the natural bounds of the model, the stiffness' would then be much less than 1E16.

If your model has contact check the contact stiffness (in solution output) when using MKS units.  There may also be an warning about these. 

What results are changing?  By how much?

If no contact, turn on the connections (Solution Information option) and see if there is a difference in the scoped region between the two unit systems.