Contribute compatibility file missing

["Nick Barling" <webforumsuser@xxxxxxxxxxxxxx>]

Hi all,

 I am getting an error in DW CS3 that says 'The file required for Contribute 
compatibility does not exist on the server.  Would you like to turn Contribute 
compatibility off?'

 I get this warning when I enable Contribute in the site definition and then 
try and check-in a page.

 Does anyone know what this warning means and how do I fix this error?

 Thanks in advance for any suggestions.