Bootstrap Modal doesn't close

Bootstrap Modal doesn't close

HTML:
<div id="im_modal" class="modal hide fade" tabindex="-1" role="dialog"
aria-labelledby="Image" aria-hidden="true">
<div class="modal-footer">
<a type="button" class="btn pull-left"
href="javascript:close_preview()">Cancel</a>
<button type="submit" class="btn btn-primary pull-left">OK</button>
Javascript:
function close_preview() {
$("#im_modal").modal("hide");
}
The function close_preview is being called, but doesn't close the modal.