Could not connect to database: the login fails.

This will only happen when you're trying to connect to a MSSQL server that is running in windows authentication mode. ContactWise needs mixed mode in order to work. If this pops up in postgres or oracle, make sure that the ODBC DNS entry you created in windows is giving you a live connection.

Could not create database: Cannot perform this operation on a closed dataset.

'Closed dataset' is a bit of a misleading way to term this error. In the case of the 'Login fails' error above, it's because you can't access the server. A closed dataset error means you aren't allowed to create tables or alter existing databases. It will also throw this error when you can't connect to the server. ContactWise recognizes any failure to create the database as a closed dataset error, regardless of what caused it. In the case of oracle or postgres, the database container you're trying to use doesn't exist. This error will also be thrown when you're trying to create a new database using a database name that already exists. Remember, in postgres, you have to create the container name before you create the database.

Could not perform this operation on an open dataset:

This error should only throw during the Go Remote operation. It means that the table structure has been changed, a bug that sometimes comes up from time to time. The columns get reordered and the go remote program doesn't know how to go remote with columns that are in a different order than what it expects. This error doesn't mean your database is corrupt, it just means that an admin needs to go and move the columns back into their original order. Contact support for information on how to repair this issue.