Why do I get "database is unavailable" when using an Easysoft ODBC driver with a web server?

The most likely reason for this is database file permissions. The web server may well be running as a user who has severely restricted permissions.

The solution is to change the database entry in the ODBC data source to specify a remote connection, as described in How do I connect to a remote server by using TCP? The database connection is then made as the user the InterBase or Firebird server is running as. This user will have the necessary permissions.