Whilst checking our client's backups I've come across several common problems so I thought I would share the solutions.

Errors: Could not access portions of directory System State\COM+ Class Registration Database. 
You may not have permission to open the file, or the directory may be missing or damaged. 
Please contact the owner or administrator. "

Error: Could not access portions of directory System State\Registry. 
You may not have permission to open the file, or the directory may be missing or damaged. 
Please contact the owner or administrator. 

Error 0x80042316

Error returned while creating the volume shadow copy:0x8007000e.

Error returned while creating the volume shadow copy:Not enough storage is available to complete this operation.

Error: The device reported an error on a request to write data to media.

Error reported: Invalid command.

Error: D: is not a valid drive or you do not have access.

Error: WATSONSVR\Microsoft Information Store\First Storage Group is not a valid drive or you do not have access.

Error: Event 8001 8019 NTbackup error occurred periodically in event viewer.  These errors may occur if your Exchange Server 2003 database files are located on the same drive as the Windows Server 2003 operating system.

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You need to follow these suggestions to achieve successful results:

Suggestion 1: First of all, please temporarily disable all anti-virus and anti-spam software like Trend Micro Messaging Security and OfficeScan on the SBS server.

Suggestion 2: Use the suggested step in KB820272 if your Exchange Server 2003 database files are located on the same drive as the Windows Server 2003 operating system.

Backup operation fails when you back up Exchange Server 2003 databases and System State Information at the same time

http://support.microsoft.com/kb/820272/en-us

 Method1: Perform Seprate Backup oprations

Configure separate backup operations for the System State and the Exchange Server 2003 databases. After the System State backup is complete, the storage group is unfrozen and may be backed up successfully.

Method 2: Move the Exchange Server 2003 Database Files

Move the Exchange Server 2003 databases to a drive other than the operating system drive. This permits you to back up both the Exchange Server 2003 databases and the System State information at the same time.

Suggestion 3: Change the USB drive to local/remote hard disk to clarify if it is a USB drive issue.

Change the USB drive to local/remote hard disk to clarify if it is a USB drive issue. Sometimes this could mean problems with the USB disk subsystem (controller/Disk drives) and we may suggest customers to get updated firmware and drivers for the controller.

Suggestion 4: This issues happens if the following services are started

1. Microsoft Software Shadow Copy Provider

2. Volume Shadow Copy

By default these services are set to manual, so let's stopped these two services and try backup again.

Suggestion 5: On SBS server if you are performing an incremental and differential type of backup and circular logging is enabled you won't be able to complete job successfully, to achieve the successful result you need to disable the circular logging.

Note: Most common mistake you need to check when selecting the exchange database in Ntbackup utility, please navigate to Microsoft Exchange Server -> Server Name -> "Microsoft information store" and select it from the left pane. Please do not select the exchange database folder from the program files.