Error 9001, Severity: 21, State: 1 The log for database 'DB_NAME' is not available
These symptoms sometimes occur when AutoClose in database settings is turned on. Deactivate it and try again. I had the same errors with 2008R2 Express Edition vor a Sharepoint Foundation 2010 database instance a short time ago. I investigated and found for example:


http://www.sqlservercentral.com/Forums/Topic1037190-1550-1.aspx
http://social.msdn.microsoft.com/Forums/sqlserver/en-US/acfacc5e-bf1e-474d-825e-9eff927e0311/the-log-for-database-xtrans-is-not-available
https://stackoverflow.com/questions/15771371/the-log-for-database-x-is-not-available


Then I changed "AutoClose" to off and the troubles had gone. Before that, I had to take the affected databases offline and online again.

The errors occured everytime a scheduled job did a DBCC CHECKDB. A manually started check of the databases did not show any error.