user is not able to access the database "msdb" under the current security context.

Symptoms when the guest user is disabled in the msdb database

USE msdb;
SELECT prins.name AS grantee_name, perms.*
FROM sys.database_permissions AS perms
JOIN sys.database_principals AS prins
ON perms.grantee_principal_id = prins.principal_id
WHERE prins.name = 'guest' AND perms.permission_name = 'CONNECT';

GO

If you receive a result set that resembles the following, the guest user has the necessary permissions. 

 

If you receive either an empty result set or if the state_desc shows DENY in the result set that is mentioned here, the guest user is disabled in the msdb database. You may receive error 916 when you connect to a database.

How to resolve the issue

USE msdb;
GRANT connect TO guest;
GO

http://support.microsoft.com/kb/2539091/en-us