File attachmenrts are not shown since upgrade from 6.14 to 7.2

Hey guys
I've upgraded my drupal 6.14 site to 7.2 (to 7.0 befor 7.2). Now I have the problem that I can't see any file attachment on any node.
I use different Content types but every time the Field "File attachments" (Label "Above" and Format "Table of files") is displayed. Does anyone have a sugestion how to fix this?

The sourcecode on the old site (drupal 6.14) looks like this:

<table id="attachments" class="sticky-enabled"> 
 <thead><tr><th>Attachment</th><th>Size</th> </tr></thead> 
<tbody> 
 <tr class="odd"><td><a href="http://example.com/XYZ/?q=system/files/ESX.pdf">ESX.pdf</a></td><td>155.31 KB</td> </tr> 
</tbody> 
</table> 

The sourcecode on the new site (drupal 7.2) like this:

<div class="field field-name-upload field-type-file field-label-above"><div class="field-label">File attachments:&nbsp;</div><div class="field-items"></div>

When I try to manage the field "File attachments" it says

There is data for this field in the database. The field settings can no longer be changed.

It only works with new attachments. So if I add any attachment after the upgrade it works fine.
Regards
Philip