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When you try to add a file type to the Registered File Types list, you receive the following error message, even if you cannot find the file extension in the list:

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Microsoft Knowledge Base Article

This article contents is Microsoft Copyrighted material.
©2005-©2007 Microsoft Corporation. All rights reserved. Terms of Use | Trademarks

Article ID: 129050 - Last Review: January 19, 2007 - Revision: 1.2

Err Msg: The Extension '.<ext>' Is Already In Use By File Type '<Name>'

System TipThis article applies to a different version of Windows than the one you are using. Content in this article may not be relevant to you. Visit the Windows Vista Solution Center
This article was previously published under Q129050

SYMPTOMS

When you try to add a file type to the Registered File Types list, you receive the following error message, even if you cannot find the file extension in the list:
The extension '.<EXT>' is already in use by file type '<Name>'. Choose another extension.

CAUSE

Multiple file types can be registered to one application. In this case, the file type does not appear in the Registered File Types list, but instead appears in the details for another registered file type.

For example, the registered file type Microsoft Word 6.0 Document can contain .RTF, .DOC, and .DOT extensions. Even though these file types do not appear in the Registered File Types list, they are registered to Microsoft Word 6.0.

RESOLUTION

To change the association of a file type that does not appear in the Registered File Types list, follow these steps:
  1. In My Computer or Windows Explorer, click a file of the appropriate type, and then press and hold down the SHIFT key while you right-click the file.
  2. On the menu that appears, click Open With.
  3. If you are prompted to, enter a description for the file type. In the "Choose the program you want to use" box, click the program you want to use for this file type.
  4. If the "Always use this program to open this file" check box is not selected, click the check box to select it.
  5. Click the OK button.

APPLIES TO
  • Microsoft Windows 95
  • Microsoft Windows 98 Standard Edition
Keywords: 
kbenv kberrmsg kbprb KB129050
       

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