The attached SW14 assembly file has all the parts made “in context”.  The part “skirt short” as undefined because it is not fixed in space.  It was not showing this error before I successfully moved its sketch plane and then successfully mirrored it to the other end of the table.  My attempts to fix have failed.

The sketch is fully defined and all the external references seem consistent with other parts.  I tried:

1. mating the face of the part to the correct offset from legA (the new “plane sketch” position); no error msgs but no change after rebuild.
2. rolling back to below skirt short, deleting the extrusion, opening a new sketch on the “plane sketch”, converting the “skirt short” sketch, cutting it in half to allow for the following mirror operation, but this failed when I couldn’t select the mirror plane and other errors occurred. I closed without saving.

Bevin