If TaxCalc loses contact with, or has never been able to connect to a database, you will receive a similar message to the below:

This means that the connection to the database cannot be established. To resolve, you will need to know whether TaxCalc works on the server machine (the machine where the database is held) or not. Please see the below links for further clarification. 

Cannot connect to DB - Server machine

Cannot connect to DB - Client machine