When changing the Microsoft SQL Server 2005 Service Account you might get back this rather alarming error message box:

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WMI Provider Error
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The process terminated unexpectedly. [0x8007042b]
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OK  
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This is related to the problem documented in Books On Line on the page titled: 'Start and Restarting Services' (accessible in the index as 'starting SQL Server').  I quote from the paragraph that describes the problem:

"If SQL Server 2005 is shut down with open shared memory or a named pipe connection and is then restarted with the credentials of a different user, it may fail to start. This is normal behavior for connection handles controlled by the operating system. To restart SQL Server, end all SQL Server client processes manually or by restarting the computer. Possible errors include "Server shared memory provider failed to initialize. Error: 0x5" and "Server named pipe provider failed to listen on [ \\.\pipe\sql\query ]. Error: 0x5" (The pipe name may vary.)"

The problem described in the paragraph above manifests itself as the 'The process terminated unexpectedly. [0x8007042b]' error message box when using the SQL Configuration Manager to change the SQL Server (Engine) Service Account.  The workaround, as stated, is to close all client processes (connecting to the named pipe) or reboot the server. 

The problem is caused by an Operating System limitation which has been removed in Windows Vista.  In Windows Vista a change has been made to allow the tear down of a named pipe listener when only the server side connections are closed.  In Windows 2003 and earlier, there is a requirement to close down the client side connections as well, and this requirement prevents sqlservr.exe from creating a new properly ACLed named piper listener when the service is restarted with new Service Account credentials.

I hope you will find this post using your favorite search engine should you be panicked by this error message in the wild.  I will also push to get a KB article written with this information in it.