I was using sqlcache dependency in my dot net project file yesterday...and today somehow I cannot connect to my local database.
Msg 945, Level 14, State 2, Server ServerName, Line 1 Database 'msdb' cannot be opened due to inaccessible files or insufficient memory or disk space. See the SQL Server errorlog for details.
To work around this problem, you must change the DACL on the user database file to use the new service account. Then, you must restart the service.
To change the DACL on the file, follow these steps: 1. Log in to SQL Server as the administrator of the computer that is running SQL Server 2005.
2. Locate the database file.
3. Right-click the file, and then click Properties.
4. Click the Security tab.
5. Click Add. Type the name of the service account in my case it is "COMPUTERNAME\ASPNET". Click to select the Full Control check box, and then click OK.
found this solution at
http://support.microsoft.com/kb/899436