DataType - The system has encountered an error - APNX-1-4198-000

I'm facing the following error when attempting to create a datatype. This pops up whenever I select the data source, regardless of the selection. I did not show the expression fully because it is incredibly large. 

The application has just been created, with only one empty data store and some interfaces. 

What could've caused this? Is it a system error? Does it have any solution?