Registry filter may fail on Windows XP-based Embedded operating system

Symptoms

The Registry Filter is an Embedded-Enabling Feature used to preserve selected registry keys and values on Microsoft Embedded operating systems that use EWF (Enhanced Write Filter) or FBWF (File-Based Write Filter). These two write filters prevent volume or file system updates, respectively, and the Registry Filter is used to allow specific registry settings to "write through" and be preserved even with an enabled write filter. The Registry Filter is especially important when the embedded systems are used in a network Domain.

On the Windows XP-based Microsoft Embedded operating systems in the Applies To section with an enabled write filter and implemented Registry Filter, the Registry Filter may fail to properly preserve registry values. Two specific values supported by Microsoft, the domain secrets key and the TSCALs key may fail to persist which can result in a loss of domain participation or inadvertently running out of Terminal Service CALs. This issue can potentially affect the preservation of user-configured registry keys as well.

Cause

A problem in registry management was discovered during Windows Vista testing that was corrected for Windows Vista and later operating systems. Unfortunately this problem was not corrected in Windows XP operating systems which include those operating systems in the Applies To section.

Resolution

WES 7, POSReady 7, and later Microsoft Embedded products do not encounter this problem; Microsoft recommends migration to one of these system if you are encountering problems with the preservation of registry values when using the Registry Filter component.

More Information

The identified problem with registry management is very narrowly focused and is extremely timing dependent, sensitive to high CPU usage, and very difficult to reproduce. It only affected the way that the Registry Filter works on XP-based Embedded systems. 
Properties

Article ID: 2720082 - Last Review: 4 Jun 2012 - Revision: 1

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