This error typically occurs when the Module Server service is not running. The Module Server has to be running and the appropriate modules available on the machine. This means both the Module Server and the client modules need to be on the same machine if Extraction, Classification, etc are being used in the profile.. Please check and ensure this service is installed and running and please try again.
Regarding the required validation, when a document type is assigned, the form needs to be validated since CWC knows nothing of doc type validations and this requires a back-end call which involves the Module Server. In addition, if you try to submit a form that has validation errors, then you will get a prompt that validations are needed first before submitting. This is a requirement. After that, you can ignore and submit anyway if you want to submit the form data with validation errors.
Hope this helps.