CORRUPT ACCESS DATABASE FAQ

   Jetlock.doc           Understanding Microsoft Jet Locking White Paper
   Readme.txt            Readme file with Installation information
   LDBView.exe           LDBView utility
   Dblck.exe             Self-extracting executable that contains the setup files for DBLock
   Msldbusr.exe          Self-extracting executable that contains Msldbusr.dll and associated files.

Typical Causes of MDB File Corruption

There are three main causes of corruption in Access/Jet mdb files.

Database is Suspect/Corrupted Due to Interrupted Write Operation

You should always quit Access properly by clicking Exit or Close on the File menu. If a database is open and writing data when Access is abnormally shut down, the Jet database engine may mark the file as suspect/corrupted. This can happen if the computer is manually turned off without first shutting down Windows or if power is lost. Other situations may not shut down Access but may still interfere with Jet's writing of data to the disk while the database is open. This can happen, for instance when networks experience data collisions or disk drives malfunction. If any of these interruptions occur, then Jet may mark the database as potentially corrupted.

When Jet begins a write operation, it sets a flag, and resets the flag when the operation is completed. If a write operation is interrupted, the flag remains set. When you try to open that database again, Jet determines that the flag is set and reports that the database is corrupted. In most cases, the data in the database is not actually corrupted, but the set flag alerts Jet that corruption may have occurred. In cases such as this, compacting and/or repairing the database can typically restore the database. Fortunately, there are ways to determine which user and workstation was responsible for marking the file as suspect. See the "How to Determine What Users/Workstations Are Causing the File to be Marked Suspect" section later in this article.

Faulty Networking Hardware

In this case, the file corruption does not involve the Jet database engine; rather the file is literally corrupted by some outside cause. The cause can be one or more links in the hardware chain between the computer that the database resides on and the computer that has the database open. This list includes, but is not limited to, network interface cards, network cabling, routers, and hubs.

Hardware-based corruption is typically indicated by .mdb files that cannot be restored through the use of compacting, repairing, or Jetcomp. Hardware corruption will typically recur until the responsible hardware is repaired or replaced.

Opening and Saving the MDB File in Another Program

There is no way to recover a .mdb file that was opened and then saved in a program other than Access. For example, Microsoft Word allows you to open an Access database and then save it (although it serves no good purpose to do so because if you open an MDB file in another program, all you can see are extended characters). Saving the file in this manner will cause the .mdb file to prompt you for a database password when you try to open it in Access even though the file may have never been password-protected in Access. The password prompt occurs in such cases because the first byte range that Access checks when it opens a file is where the database password would be. If that byte contains corrupted data, Access treats the file as being password protected. Even if there were a way to get around the password prompt in this case, the database would still be unrecoverable because the binary structure is scrambled and therefore unreadable to Access. Recovering a backup copy of the file is the only solution in this case. For additional information about this issue, click the article number below to view the article in the Microsoft Knowledge Base:

223043 ACC: Database Password Appears Even Though It Was Never Set

How to Determine What Users/Workstations Are Causing the File to Be Marked Suspect

You can determine which workstation and user caused Jet to mark a .mdb file as suspect with the LDBView utility, which is available by downloading Jetutils.exe from the following Microsoft Web site:

http://download.microsoft.com/download/access97/utility1/1/WIN98/EN-US/JETUTILS.EXE

For additional information about the Microsoft Jet Utilities, click the article number below to view the article in the Microsoft Knowledge Base:

176670 ACC: Microsoft Jet Utilities Available in Download Center

Ldbview let you observe which users are currently logged into the database, as well as any users that may have left the file in a suspect state.

Steps That You Can Take to Help Prevent Corruption

• Avoid losing power during database writes. Losing power can cause the database to be left in a suspect state.
• Avoid dropping network connections.
• Avoid abnormal termination of Microsoft Jet connections such as power loss, manual shutdown, having Task Manager shutdown the application, and so on.
• When programming, close all Data Access Object (DAO) and ActiveX Data Objects (ADO) objects that you have open. Examples include Recordset, QueryDef, TableDef, and Database objects.
  
• Fatal system errors almost always cause abnormal termination. If your database is prone to fatal errors, you should resolve the errors before the database becomes too damaged to open or recover.For additional information about the Microsoft Jet Utilities, click the article number below to view the article in the Microsoft Knowledge Base:

  148424 ACC: Troubleshooting Fatal System Errors in Microsoft Access 95 and Microsoft Access 97

• Compact the database often.
  
  IMPORTANT: Do not run the Repair Database command in Access 97 unless Microsoft Jet prompts you to do so.
• Do not run IPX on Windows NT Server where Jet databases are located across the network and the client is Microsoft Windows 95 with IPX/SPX. Instead, run TCP-IP on the Windows NT Server and a dual protocol stack of IPX and TCP-IP on the Windows 95 client. Windows NT to Windows NT with IPX/SPX will not cause the problem, nor will Novell to any client.
• Avoid a large number of open and close operations in a loop (40,000 successive open/close operations to over 1,000,000.