This is no doubt too late to help with the problem you were having but may help both of us understand Simulation a bit better. (We just got a seat to go along with a seat of ANSYS). What is the magnitude of the force parallel to the surface? There will always be some (tiny) forces just due to the nature of FEA. If you have forces that are significant, say a few % of the force perpendicular to the surface, then I would suspect that it is due to deflections causing your surfaces to rotate relative to the original normal direction.
Since friction really does happen in the real world, you might also want to add a low friction coefficient, say 0.1, to see how the result changes. You could then try 0.2 or 0.3 to see how significant friction will be in real life. (These values assume you have solid-solid contact, not a lubricated bearing surface.)
Thanks for your input. Since my original post I have worked out what was happening. The reason why Simulation was showing a contact force parallel to the flat surface was because the nodes along one edge of the surface were also included in a different contact set which was oriented perpendicular to the original surface. The nodes along the edge had contact forces applied from the two different contact sets. This is correct but the way it is presented is perhaps a little misleading, at least I found it to be. You have to remember that when you list contact forces by selecting a surface then all the edges are also included and any forces applied to these edges due to other contact set definitions will be included. It seems you cannot list the the contact forces due to a single contact set definition independantly.