Error 44 connecting to the database

Client fails with Error 44 connecting single-user direct connection (No server is running for the database).
Client fails with Error 44 connecting self-service shared memory  (Without the Database Listening port -S).

Multiple Progress OpenEdge Versions are installed

The client and the database do not have the same Major and Minor release numbers.  Major and Minor release numbers must be the same for the client and the database when using a shared memory or single user connection.

The client version, or Specifically the version of the executable that the Client Session is running will need to be changed to match:

1. The Database Major Minor version to connect Self-Service or single user
2. The Database Major version or one Major version higher to connect Client-Server (-S).

To understand version numbers and connectivity rules, refer to Articles:

How to determine the Progress version based on Error 44   
How are Progress and OpenEdge Versions are Numbered?   
What Type of Database Connection is possible from Client to Server when the Progress versions differ   
 

Progress Article:

 What causes Error 44 when accessing an OpenEdge database?