Take it to a different station. They may have had a flaky machine or a bad cable. If it happens at the next shop ask wtf is going on and go from there. You might have a loose wire in/around the OBD2 plug too although I've NEVER heard of this sort of thing happening.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.