Several times I encountered this situation. Is not there any check when a comment request sent to user if it was already commented? Last time I had a comment request to 'A Rose' by Ventiol, which I commented at first.
Any image that has not recieved many comments is automatically put out for comment requests. I often get ones I have already commented on. I suspect you get these a lot as you comment a lot. Just tick the box and press 'process checked'. You are not expected to leave another comment.
Actually you're not expected to leave another comment. Unless you find something more you really really wanted to say.
elektronist, comment requests are sent completely randomly, there is no check for anything other than that the member has logged on within the past 24 hours.
If *caedes can code it to not send to a member who has already commented on that image, that would be a logical kind of thing to do, so it's a good suggestion.
In the meantime, just click the "ok" button to get rid of it, and don't worry about it further.