"Pictures not found" in OE

I sometimes insert a midi music file when sending emails with OE 6 (format>background>sound). However, when I click the 'Send button I get the message: 'One or more of the pictures in this message could not be found. When you send this message these pictures will not be included.' The fact is that I have not included any pictures in the messages but rather midi files only. Also, the midi music files ARE sent and received too. Could someone tell me why this irrelevant message is popping up, and how I might discourage its reappearance? Many thanks.

 

Thanks, Pete. While I didn't yet solve the difficulty I'm having, I did find the link you gave very useful. I managed to resolve other issues I was having with OE 6 by using the resources provided. Much appreciated.

Tom