Symptoms
When you perform a full backup of a database in Microsoft SQL Server 2005, you may receive an error message that resembles the following:

Backup failed for Server ‘ComputerName\SQLInstanceName’.(Microsoft.SqlServer.Smo)
Additional information:
System.Data.SqlClient.SqlError: The backup of the file or filegroup “sysft_ FullTextCatalog” is not permitted because it is not online. BACKUP can be performed by using the FILEGROUP or FILE clauses to restrict the selection to include only online data. (Microsoft.SqlServer.Smo)If you perform a full backup of a database in SQL Server 2005 Service Pack 2 (SP2), you may receive an error message that resembles the following:

The backup of full-text catalog ‘FullTextCatalog’ is not permitted because it is not online. Check errorlog file for the reason that full-text catalog becomes offline and bring it online. Or BACKUP can be performed by using the FILEGROUP or FILE clauses to restrict the selection to include only online data.
Resolution
This behavior occurs because a full-text catalog in the database is not online. To perform a full backup, SQL Server 2005 requires all the database files andfull-text catalogs in the database to be online.
The full-text catalog may be online because one or more of the following conditions are true:The full-text catalog folder is either deleted or corrupted.You did not enable the database for full-text indexing.The database is restored from a Microsoft SQL Server 2000 database backup. Therefore, the folder of the full-text catalog in the database does not exist on the server where you restore the database.The instance of SQL Server 2005 that you are running was upgraded from SQL Server 2000. However, the full-text search service cannot be accessed during the upgrade.The database is attached from somewhere. However, you specify the incorrect location for the full-text catalog folder during the attachment.Note In SQL Server 2005 SP2, the reason that the full-text catalog is not online is logged in the SQL Server error log. See the SQL Server error log for the specific cause of this behavior.