The attach operation cannot continue because another object in this farm already contains the same ID. Each object in a farm ...

The attach operation cannot continue because another object in this farm already contains the same ID. Each object in a farm must have a unique ID. In order to proceed with the attach operation you must assign a new ID to this database. To attach this database with a new ID, use the Mount-SPContentDatabase command with the -AssignNewDatabaseId parameter. Note that if this new database and an existing database contain the same site collections, attaching this database will likely result in orphaned site collections due to conflicts between the two databases.