I've had issues selecting curves in various situations. This specific one includes using a projected curve as a guide curve in a loft. I can't select it through the tree, in the viewport or by using the selection manager. To get around this, I create a 3D sketch, click the curve in the tree (because it sometimes can't be selected in the 3D viewport) and Convert Entities. That 3D sketch is then fully usable. Anyone else see this behavior?