Solidworks gives me an error when I try and place both of these spline control points on the same plane.
The line will have a zero length on one axis only, but that doesn't mean the line is zero length.
..Hello Scott.. yeah... does not makes sense (or does it??).. so, just constrain the Spline line Parallel.. (image)
I can constrain the line to be "On Plane" but not the two individual points. Your solution works as well.
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