Method 1: Dismount all databases in the storage group
Use this method if the event ID 9840 that was logged on the Exchange 2007 server contained error code 2403.
To dismount all databases in the storage group, follow these steps:
1. Click Start, point to All Programs, point to Exchange Server 2007, and then click Exchange Management Console.
2. Expand Server Configuration, and then expand the storage group that is listed in the event ID 9840 message that was logged on the Exchange 2007 server.
3. Right-click each database in that storage group, and then click Dismount Database.
4. Click Yes to confirm the operation.
5. After the dismount operation is complete, right-click the database again, and then click Mount Database.
6. Try to perform the backup operation that resulted in event ID 9840.
If this method does not resolve the problem, try method 2.
Method 2: Restart the Microsoft Exchange Information Store service
Use this method if the event ID 9840 that was logged on the Exchange 2007 server contained error code 1293. Use this method if Event ID 9607 was logged on Exchange 2003. Additionally, use this method if method 1 did not resolve the problem.
To restart the Microsoft Exchange Information Store service, follow these steps:
1. Click Start, point to All Programs, point to Administrative Tools, and then click Services.
2. Right-click Microsoft Exchange Information Store, and then click Restart.
3. Try to perform the backup operation that resulted in event ID 9840.
http://support.microsoft.com/kb/930800
Finally in order to verify that no snapshots are present, follow these steps:
1- Open a command prompt on the Exchange server and type the command "Vssadmin list Shadows"
2- If a snapshot exists, it will be listed. Before attempting to delete the snapshot make a note of the time at which it was taken. This will help to determine if the orphaned snapshot was created during or outside a backup. If the snapshot was created outside a backup, check for scripts or application that could have created it (for example some applications take snapshots by creating Scheduled Windows tasks).
3- Make a note of the ShadowId and use command "Vssadmin delete shadows /Shadow=<ShadowId>" to delete it
