Document Information Panel Failed to Load - Location attribute invalid value

Hi all,
 
    I have a series of webs in a site collection (about 1000) that were created from a site template that included a Document Library.  Whenever an Office file is uploaded and then edited from the SharePoint library, Excel/Word comes up with an error:
 
Required Properties - To save to the server, correct the invalid or missing required properties.

You hit Edit Properties and get:
 
The form cannot be opened. To fix this problem, contact the form designer.
 Form template: http://server/sitecollection/site/proppanel.xsn
 The XML Schema for the form template has an invalid value for the following attribute: location
 

The content type is valid and has a a plain old empty .doc file. (Update - have updated this to an empty .dotx file with no effect)
 
Its reproducable on our DEV, TEST and PROD environments.
 
New additional document librarys created in the Web with the same Content Type work fine.
 
The DIP settings for the Content Type are at the default (not a custom DIP).  I have tried setting a custom DIP, and then setting it back - but the error returns.

I assume this problem has been propogated by the site template - but I need to know how to fix it for the 1000 existing sites (via PowerShell etc.).

This problem still occurs after SP1 and Dec 2011 CU.

Any ideas where the Location attribute is that has the invalid value is coming from?

Any help/suggestions would be appreciated!

 
Cheers,
 
    James.