At the open order could not be executed

Hi,
Have anyone ever encountered “At the open order can not be executed” for an order to exit an existing position at OPG/MKT.
This happened to me today in a paper trading mode. The order was placed few hours before market open and the cancel message above was received 31 seconds after market open. Other OPG/MKT that I placed at the same time were filled 2-3 seconds after open.
Is this something that can happen in live?
Thanks, N
 
IB paper trading does not simulate MKT OPG orders properly.

I've never had a live MKT OPG trade not fill (unless it's a buy order and there's insufficient buying power).
 
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