Hi,
It looks like the path that i have specified is incorrect. If you are on a mac you will need to place the file in these two locations:
Hard disk: Users: <Your User Name>: Library: Application Support: Adobe: Dreamweaver CS4: en_US : Configuration: Behaviors: Actions: WA Validation Toolkit: Apply Client Validations
And
Hard disk: Users: <Your User Name>: Library: Application Support: Adobe: Dreamweaver CS4: en_US : Configuration: Commands
The WAFV_Required_C.js should exists in both locations.
Let me if you still get this error after replacing the files.