My best picture this week

Hello

I got this message by mail:

"Dear rutan6,
Your entry .
has been disqualified from the challenge called My best picture this week for the following reason:
During the submission phase of this challenge, pictures present here may not be present in any other challenge.
Regards,
Challenge Host"

but ithe picture i sent to this Challenge was sent only to this challenge
can someone explain me the reason for the disqualification
and also why i was disqualified after the submission phase finished?
in a way i cant fix the problem if there was one
thanks
Rutan6