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IIS 6.0: ISAPI Filters for Earlier Versions of IIS May Not Load

This article was previously published under Q327611
In Internet Information Services (IIS) 6.0, you may not be able to add global ISAPI filters designed for IIS 5.0 and earlier versions. The filter will show as added, but you will always see a red arrow next to the filter. This red arrow may still appear after you restart IIS.
IIS 6.0 can operate in one of two isolation modes:
  • IIS 5.0 isolation mode
  • IIS 6.0 worker process isolation mode

Global ISAPI filters designed for previous versions of IIS work the same way they work in earlier versions if you are operating in IIS 5.0 isolation mode. However, the same filter may not work in IIS 6.0 worker process isolation mode because the SF_NOTIFY_READ_RAW_DATA notification is not supported in this mode.
With IIS 6.0 running in worker process isolation mode, when you load an ISAPI filter designed with the SF_NOTIFY_READ_RAW_DATA notification and you then request a Web page, the following event may be logged in the application log:

Event Type: Error
Event Source: W3SVC-WP
Event Category: None
Event ID: 2261
An attempt was made to load filter
'C:\WINDOWS\system32\inetsrv\iismon\IISMonHi.dll' but it requires the SF_NOTIFY_READ_RAW_DATA filter notification and this notification is not supported in Worker Process Isolation Mode. For more information, see Help and Support Center at

If you cannot redesign the filter, you can work around this problem by running IIS in IIS5.0 isolation mode.
For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
Q311852 ISAPI Filters with SF_NOTIFY_READ_RAW_DATA in IIS 6
iis 6 iis6 iis 5 iis5 iis4 iis 4.0

Article ID: 327611 - Last Review: 12/03/2007 21:27:16 - Revision: 3.4

Microsoft Internet Information Services 6.0

  • kbprb KB327611