Always remember to include the mraid.js in the head section of the banner. It does not matter if the file is not present in the folder, it is just for detection purposes. Here is code snippet on how should it look:
<head> <meta charset="UTF-8"> <script src="mraid.js"></script> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="HandheldFriendly" content="True" /> </head>
Info: For full MRAID specifications please visit http://www.iab.net/mraid.