When registering a database data store in ArcGIS Server Manager, the following error occurs:
"Invalid database connection"
Attempting to register the same database data store in ArcGIS Desktop returns the error:
"The data item is inaccessible"
Viewing the ArcGIS Server logs shows this error message:
"The connection property set was missing a required property or the property value was unrecognized. Cannot connect to database because the database client software failed to load. Be sure the database client software is installed and configured correctly."
The machine where ArcGIS Server is installed is missing the 64-bit client libraries for the specific DBMS to which the connection is being made.