"The add-in could not be installed or loaded" error message when you start Outlook 2000

After you upgrade your Microsoft Windows Millennium Edition (Me)-based computer to Microsoft Windows XP and then start Outlook 2000, you may receive the following error message:When you click OK in this error message, Outlook 2000 opens.

To resolve this issue, rename and re-create the Outlook Extend.dat file. To do this, follow these steps:

1. Quit all programs that are running.
2. Click Start, and then click Search.
3. Click All files and folders.
4. In the All or part of the file name box, type extend.dat.
5. In the Look in: list box, click to select your hard disk.
6. Click Search.
7. In the search results, right-click the Extend.dat file, and then click Rename.
8. Type Extend.old, and then press ENTER.
9. On the File menu, click Close to exit the Search Results window.
10. Restart Outlook 2000.

The Extend.dat file is re-created when you restart Outlook 2000.

The Extend.dat file is a binary file that caches registry entries for third-party product extensions. The Actext.dll is an extension installed by ACT! software to provide access to the ACT! address book.

The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.