File Upload Required but not Required

Hi guys

I have a form which has the option of uploading a file - in particular pdf's and word docs.

The form works fine when users complete all fields. But when it is partially completed it comes up with an error. Through trial and error I have narrowed it down to the fact that if the user does not upload a file then the form returns the error.

To me this looks like the file upload is a required field.

The problem is, is that the file upload has not been indicated as a required field - I have gone through both the wizard and the code (turning the required field button on and off) with no success.

The code looks like this (and to my untrained eye looks like it is not making this field required):

<div class="form_item">
<div class="form_element cf_fileupload">
<label class="cf_label" style="width: 200px;">Upload Here</label>
<input class="cf_fileinput cf_inputbox" title="" size="20" id="file_12" name="file_12" type="file" />

</div>
<div class="cfclear"> </div>
</div>

Does anyone have any ideas on how to make this a non-required field or where I am going wrong please?

Many thanks