Trades ': rejected market buy 0.01 EURUSD

I had an EA perform a (scalping) test on two demo accounts. It went well for a few hours until the message "Trades '4113XXXX': rejected market buy 0.01 EURUSD" appeared. I could also no longer manually place positions, only close. What is the reason for this and can this also happen live?
I found it. Admiral Markets is blocking trading. I did the same test on ICmarkets (MT5) with so many positions that the steam came out of the computer. There were no problems there.