Fastener errors in mechanica

I created 4 triangular sheetmetal parts (2 parts, 2 mirrored parts) with a flat wall bend at one side. These triangular parts are then assembled onto a bracket at the 4 corners. On the assembly level I cut out bolt holes into each triangular part (1 cut has all the holes). Then I put the fasteners in, define a preload, etc. I'm getting this error:

"The fastener references are not oriented correctly. This happens if the associated surfaces are not oriented such that the normal of the top reference surface points away from the normal of the bottom surface."

The thing is, I'm only getting that error on the mirrored parts, not the original parts. The references shouldn't change, and I've redefined the fasteners twice. Can anyone shed some light into what that error is telling me? It's not very intuitive, considering the faces of the two surfaces involved are parallel.

Thanks,

mike