Error: “The database has been locked by another user.” when opening a database

Symptom: When I try to open my database, I receive the Error: “The database has been locked by another user”
 
Product Details: 
Product Family:  Act!
Product:  Act! Pro, Act! Premium
Version: v19 and later
 

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Cause:
This will occur if the database has been locked. 
 
Solution: 
 

1. Follow the steps in the following knowledgebase article:
   
   Error: “A General lock has been placed on this database” or “The database you are trying to access has been locked by an administrator” when opening my database
   
    
2. Attempt to open the database