Thanks to Sean at https://www.limeleaf.co.uk we actually resolved this by adding the mime types. See this code snippet:
$wpbb_allowed_mime_types = apply_filters(
'wpbb_application_allowed_file_types',
array(
'application/pdf',
'application/msword',
'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
'application/vnd.openxmlformats-officedocument.wordprocessingml.template'
)
);
/* check uploaded file is in allowed mime types array */
if( ! in_array( $wpbb_filetype[ 'type' ], $wpbb_allowed_mime_types) ) {
/* upload file not allowed - add to messages */
$wpbb_messages[] = '<p class="message error">Error: CV is not an allowed file type.</p>';
return; //this return statement added by Lime Leaf on 17/7/2015 to stop the form submitting when the incorrect file type is added
}