When you try to read or to delete e-mail, or when you click "Send/Receive" in Outlook, you receive error message: "An unknown error has occurred" or "Messaging interface has caused an unknown error"

If you use Microsoft Outlook 2002, 2003 or 2007 with Windows XP or Windows Vista, when you try to read e-mail in the Microsoft Outlook Inbox, or when you click Send/Receive, you may receive one of the following error messages: When you try to delete e-mail, you may receive the following error message:

You can resolve the issue by using the Inbox Repair tool to analyze and repair the .pst file. A .pst file is a personal folders file that stores your e-mail, contacts, notes, calendar items, and other data.

The steps to use the repair tool differ, depending on whether your computer’s operating system is Windows Vista or Windows XP. Use the appropriate set of following steps to resolve the issue.

Note If the .pst file is larger than 2 GB (gigabytes), the Inbox Repair tool does not work.

This article is intended for a beginning to intermediate computer user.

You may find it easier to follow the steps if you print this article first.

Prerequisites

As you follow the steps to resolve the issue, you are asked to use a file that is typically a hidden file. In order to be able to find that file when you want it, first, show the hidden files on your computer. To do this, follow these steps:

Show hidden files in Windows Vista

1. Click Start
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   , type control in the Start Search box, and then press ENTER.
2. Click Appearance and Personalization.
3. Click Folder Options.
4. Click the View tab.
5. Under Advanced Settings, click Show hidden files and folders, and then click OK.

Show hidden files in Windows XP

1. Start Windows Explorer.
2. On the Tools menu, click Folder Options.
3. Click the View tab.
4. Under Hidden files and folders, click Show hidden files and folders, and then click OK.

Step 1: Exit Outlook

Step 2: Find the Outlook .pst file

1. Click Start
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   , type control in the Start Search box, and then press ENTER.
2. If you see Control Panel Home view, click User Accounts and Family Safety.
   
   If you do not see Control Panel Home view, go to step 2c.
3. Click Mail.
4. Click Data Files.
5. Click Personal Folders, and then click Settings.
   
   Note If there are no Personal Folders services in your profile and if you can store information such as messages, contacts, or appointments in Outlook, your information is most likely being stored in a mailbox on an Exchange Server. If this is true, information is typically backed up on the server. Contact the Exchange Server administrator for more information.
6. Note the text in the Filename box.
   
   Note You may have to click in the Filename box and then use the right-arrow key to view all the text.
7. Click OK, and then click Close two times.

Step 3: Find the Inbox Repair Tool

1. Use one of the following methods, as appropriate, for the version of Outlook that you are running.
   
   Note If you are unsure which version of Outlook that you use, open Outlook, click the Help menu, and then click About Microsoft Outlook to see the version.
   • Microsoft Outlook 2002
     
     Click Start
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     , type %ProgramFiles%\Common Files\System\Mapi\1033\ in the Start Search box, and then press ENTER.
   • Microsoft Office Outlook 2003
     
     Click Start
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     , type %ProgramFiles%\Common Files\System\MSMAPI\1033\ in the Start Search box, and then press ENTER.
   • Microsoft Office Outlook 2007
     
     Click Start
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     , type %ProgramFiles%\Microsoft Office\Office12\ in the Start Search box, and then press ENTER.
2. Find and then double-click SCANPST.EXE to start the Inbox Repair Tool.

Step 4: Use the Inbox Repair Tool

1. In the Enter the name of the file you want to scan box, type the path and file name of the Outlook .pst file that you found in step 2.
2. Click Start.
3. After the Inbox Repair Tool operation is complete, click OK.

If you can now read and delete e-mail and click Send/Receive in Outlook without errors, the problem is resolved. If you still receive an error, go to the "Next Steps" section.

Step 1: Exit Outlook

Step 2: Find the Outlook .pst file

1. Click Start, and then click Run.
2. Type control in the Open box, and then press ENTER.
3. If you see the Pick a category view, click User Accounts.
   
   If you do not see the Pick a category view, go to step 2d.
4. Double-click Mail.
5. Click Data Files.
6. Click Personal Folders, and then click Settings.
   
   Note If there are no Personal Folders services in your profile and if you can store information such as messages, contacts, or appointments in Outlook, your information is most likely being stored in a mailbox on an Exchange Server. If this is true, information is typically backed up on the server. Contact the Exchange Server administrator for more information.
7. Note the text in the Filename box.
   
   Note You may have to click in the Filename box and then use the right-arrow key to view all the text.
8. Click OK, and then click Close two times.

Step 3: Find the Inbox Repair Tool

1. Click Start, and then click Search.
2. Click All Files and Folders.
3. In the All or part of the file name box, type Scanpst.exe.
4. Change the selection in the Look in box to the local hard disk. For example, change the selection to Local Disk (C:).
5. Click Search.
6. When the search is complete, double-click SCANPST.EXE to start the Inbox Repair Tool.

Step 4: Use the Inbox Repair Tool

1. In the Enter the name of the file you want to scan box, type the path and file name of the Outlook .pst file that you found in step 2.
2. Click Start.
3. After the Inbox Repair Tool operation is complete, click OK.

If you can now read and delete e-mail and click Send/Receive in Outlook without errors, the problem is resolved. If you still receive an error, go to the "Next Steps" section.

If these methods did not help you, you might want to ask someone you know for help, or, if you use Outlook with Exchange Server, you might want to contact the Exchange Server administrator for help. You can also use the Microsoft Customer Support Services Web site to find other solutions. Some services that the Microsoft Customer Support Services Web site provides include the following:

• Searchable Knowledge Base (http://support.microsoft.com/search/?adv=1) : Search technical support information and self-help tools for Microsoft products.
• Solution Centers (http://support.microsoft.com/select/?target=hub) : View product-specific frequently asked questions and support highlights.
• Microsoft Customer Support Newsgroups (http://www.microsoft.com/communities/newsgroups/default.mspx) : Contact counterparts, peers, and Microsoft Most Valuable Professionals (MVPs).
• Other Support Options (http://support.microsoft.com/default.aspx?pr=csshome) : Use the Web to ask a question, contact Microsoft Customer Support Services, or provide feedback.

If you continue to have questions after you use these Microsoft Web sites or if you cannot find a solution on the Microsoft Support Services Web site, click the following link to contact Support: