[Stiglr]

Are you perhaps trying to Boolean a poly line object or something like that?

I think the rule is that both objects involved in a Boolean operation need to be composed of polygons (cylinders, boxes, spheres, etc.)

If it's a poly shape you're using for one of the operands, perhaps try selecting the vertices of your shape and making a convex hull object or Ordered Surface object out of it, then involving it in a Boolean operation.

Just kind of guessing from your description here...