Restrictions on Backup Operations in SQL Server

Today, I just noticed that the SQL Server backup is not generated and it is kinda weird.

After looking around from MSDN, it is found out there are some restriction from the backup operation.

– Backup not running due to any databases in offline status.
– Concurrency restriction during backup.

For more information, you may refer to the URL as below.
http://msdn.microsoft.com/en-us/library/ms175477%28v=SQL.90%29.aspx