Local Groups on a Windows 7 based client

I have a set of Windows 7 client PC's on a Windows 200 based domain. On all the Windows 7 clients, any domain member that is added to a local group is displayed as a SID. Any ideas why or how?
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If its resolving into SID,there is account which you are adding or profile corruption.

This is due to corruption of account or profile,its not able to resolve sid into names.
stu_evans99Author Commented:
Just to clarify, Windows 7 PC's all show SID names. Windows XP do not. XP PC's are showing the correct name. It looks like it's a specific Windows 7 issue.
stu_evans99Author Commented:
Another update on this. We apply domain users to local groups via the Restricted Groups setting in a group policy. On applying this GPO, we get the error "Security policies were propagated with warning. 0x6fc : The trust relationship between the primary domain and the trusted domain failed.". I have no problems adding Windows 7 PC's to our Windows 200 domain, plus I can browse network accounts and add them manually (still showing SID name). Any ideas anyone!!!!
stu_evans99Author Commented:
Solved it myself, and if I could give the points to Google I would. The problem was solved instantly once this was installed.

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Windows 7

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