Got this today:
This is a warning to let you know that we have identified activity associated with your Amazon Mechanical Turk (MTurk) Worker account that is in violation of the MTurk Participation Agreement. Specifically, your account has been flagged for using robots, scripts, or other automated methods as a substitute for your human intelligence and independent judgment, which violates Section 3(b) of the MTurk Participation Agreement
The only thing I can think of is having two hits of a batch open at once. I haven't used scripts on hits for about 3 weeks....