How to Fix the Error: “A Reference Is Required to Compile This Module” In Dynamics 365 Finance and Operations

Error: A reference to 'Dynamics.AX.ApplicationFoundation, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' is required to compile this module. CUSModel (VAR) [CUS]

This error indicates we’re trying to modify/reference code from a model (Application Foundation) other than the current model (CUS) and a reference isn’t set up between the two. 

To fix this error, navigate to Dynamics 365 > Model Management > Update model parameters.

Select the current model. The model name is “CUS” in this case. The details related to the model will be populated on the “Update model parameters” form.

Now click Next and select the model that needs to be referenced.

Once all the related models are selected, click Next and follow the dialog.