After re-syncing my entities with the database, I started running getting this error when I ran my application.

The problem was that after the sync, the package prefixes that I had given for the associations and entities had been lost within the Application Module and Entity Objects.

To solve this issue, open the files and view the xml. If there is a problem in that file, there will be an error warning within JDeveloper.

Valid XML will appear as follows:

Valid XML within an Entity Object

Invalid XML will appear as follows:

Invalid XML within an Entity Object

If there is no indicator, wait for JDeveloper to parse the XML.

Prepend all references to associations and entity objects with the package prefix that describes their location.
For example:

model.entities.EntityNameEO
model.assoc.AssociationNameAssoc

This should fix the problem!

Kevin