This article was previously published under Q288123
After you upgrade Exchange Server 5.5 to Exchange 2000 Server, you cannot connect to the Exchange Server computer using Outlook Web Access (OWA). When you try to connect to the OWA server, you may receive an HTTP 404 "Page cannot be displayed" error message.
Also, when you start the Internet Services Manager, right-click Default Web Site, click Properties, and then click the ISAPI Filters tab, if two Exchfilt.dll files appear, you receive the "Page cannot be displayed" error message. However, no errors or warnings are logged in Windows NT Event Viewer, and any other virtual directories or Web pages that are stored on the default Web site load correctly.
NOTE: If you have installed Exchange 2000 Conference Server on this computer, you will see "Microsoft Exchange Conferencing Web Component" as the name of the ISAPI filter.
When the Exchange Server 5.5 version of the Exchfilt.dll file appears, the Exchange 2000 version of Exchfilt.dll does not load.Depending on your authentication method, you may also receive the following error message:
HTTP 404 "File not found."
If you view the IIS logs for the Web site, you see that the 404 error is returned after the HTTP GET request is redirected to the Exchange/USA/Username folder. The USA folder is only used in Exchange Server 5.5, and it does not exist in Exchange 2000.
NOTE: USA is a localization folder. The USA folder may be replaced with a different language folder if OWA is set up for multiple language support.
This behavior can occur if Exchange 2000 Setup did not remove the existing Exchange Server 5.5 version of the Exchfilt.dll file from the list of ISAPI filters that are loaded by the default Web site.The old Exchange Server 5.5 Exchfilt.dll file automatically tries to redirect the user to the USA folder.
To resolve this issue:
Click Start, point to Programs, click Administrative Tools, and then click Internet Services Manager.
Right-click Default Web Site, and then click Properties.
Click the ISAPI Filters tab.
Click exchfilt, and then click Remove.
Click Apply, and then click OK.
NOTE: Do not delete the Microsoft Exchange Web Component entry on the ISAPI filters tab. This filter is the Exchange 2000 OWA ISAPI filter component and must be present for OWA to work properly.
To differentiate between the two versions of the Exchfilt.dll file, compare the location and the version stamps of each file. The Exchange Server 5.5 Exchfilt.dll file is located in %SystemRoot%\System32, by default. The Exchange 2000 Exchfilt.dll file is located in C:\Exchsrvr\Bin, by default. (For new installations, the files are located in C:\Program files\Exchsrvr\Bin, by default.) The version stamp of the files indicates which .dll is the correct version to use with Exchange 2000: