My Ameritrade GTC sell order was also cancelled..........this order has been active for about two weeks - don't know why it was cancelled today except in anticipation of a change in the status of the stock.....can't think of another reason.
Goob, I would suggest you call them with email in hand and see what they say. If they deny they have something on the fs you could forward the email to them for investigation of what is going on.
I would think someone other than myself would be interested in calling on this odd development of orders being cancelled and Goob's email.