22
Go to /include/common.php and in line 57 add "
/" before "on.png", so it looks like this:
le="color: #000000"><?php 'validate' => "<img src='". $pathIcon16 ."/on.png' alt='"._SIMPLENEWSLETTER_VALIDATE."' align='middle' />"
[EDIT] Oh, I see you have found it already! That's good!

And thanks for reporting it back!