Simulating 3 plates bolted together

I have a frame structure that I'm trying to analyze (on WF4) where I have two brackets that support a center plate. Basically, the center plate is sandwiched between the two bracket plates with two M18 bolts. In the past I have only worked with two plates bolted together which seems to work correctly out of the box, but the 3rd plate seems to confuse Mechanica and it complains about interfaces between the plates. Can anyone provide guidance on the correct way to setup this type of bolted joint?