Apheresis plasma return failure and swelling during double red blood cell donation procedure, what does this mean?

Vein perforation: The message is just the machine reporting it could not return the plasma (=failure). The swelling most likely means the needle unknowingly punctured the back wall of the vein--so drawing was OK, but return allowed it to leak out and make a bruise (that might be light in color since the RBCs were removed). Local warm compresses should help resolve it quicker.