DFS Management - Namespace Error RRS feed

  • Question

  • Hi All,

    Hoping someone somewhere has seen this before, I've googled this problem a fair bit without any joy..

    One of our DFS Namespaces is reporting the below under 'DFS Management'.

    "ERROR - An item with the same key has already been added."

    Background/What I can say -

    • Domain environment.
    • The namespace is still visible within AD, in the usual place.
    • This particular namespace has near 1500 links within it.
    • The namespace cannot be UNC'd to, unlike our other namespaces (all near-identical setup).
    • I have been able to export the contents of the config via dfsutil for reference.
    • DFS Management gives the option to 'display the namespace' which only leads to the previous error message - if I am fast enough to right-click and click on 'Properties' before the error appears, it causes MMC to crash.
    • The namespace appears to be functioning as expected right now (nearly 4 hours after it was first noticed by an engineer), however we simply cannot manage it via DFS Management (I've not tried adjusting any existing links via dfsutil).

    Any help will be greatly appreciated, let me know if you want any more details!


    Tuesday, September 17, 2019 3:26 PM

All replies

  • Hello,

    Can you provide a screenshot of your error/issue?

    Have you checked the DFSRoots folder of this particular DFS Namespace server if there are any permissions missing or that may have got corrupted?

    Best regards,


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    Tuesday, September 17, 2019 3:49 PM
  • Hi Leon,

    Thanks for the quick reply, I can't attach a screenshot yet as my account has yet to be verified; but it is exactly as the text says.

    "ERROR - An item with the same key has already been added."

    In terms of the permissions, they are all good and like for like to our other namespaces.  Even the sharing settings and whatnot are like for like.


    Tuesday, September 17, 2019 4:06 PM
  • Does this error happen to all users trying to access the DFS Management console?

    Any difference in running the console as administrator, locally/remotely?

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    Tuesday, September 17, 2019 4:52 PM
  • Hi,

    How is your situation now?

    Based on my experience, sometimes the problem is due to a duplicate entry of the msDFSR-DfsPath attribute for two or more content sets within the DFSR-globalsettings.

    Here are some recommend advices:

    We can identify the duplicates by using the ldifde command below:

    Ldifde -f c:\dfs_path.ldf -d "CN=DFSR-GlobalSettings,CN=System,DC=fan,DC=lab" -r "msDFSR-DfsPath=*" -l msDFSR-DfsPath

    This will show all content sets that have the msDFSR-DfsPath  and their values. Find the duplicate values and remove one from the incorrect content set.  Identify which DFSn target should be link the content set.


    Best Regards,


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    Wednesday, September 18, 2019 7:02 AM
  • I also suggest you to try the mentioned ways in the below article to check the health of your DFS Namespace:

    Five ways to check your DFS-Namespaces (DFS-N) configuration with the DFSDIAG.EXE tool

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    Wednesday, September 18, 2019 8:21 AM
  • Hi All,

    @Fan/Leon - a colleague has checked for duplicate entries and exhausted DFSDIAG.EXE looking for errors - however none are reported.  Event Viewer hasn't offered anything useful either.

    @Leon - I've gone over the permissions at DFSRoots and also checked AD to make sure that nothing had been quietly deleted/recreated, but all related objects are sound.

    The Namespace is still functioning in that end-users are able to use the links that existed on it, it remains unmanageable via DFS Management.


    Wednesday, September 18, 2019 12:12 PM
  • You could try deleting the dfsmgmt file under %appdata%\Microsoft\MMC to see if it helps.

    (Make a backup of the file first).

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    Wednesday, September 18, 2019 1:06 PM
  • Hi Leon,

    The issue appears regardless of which DFS enabled server we use.

    We've logged a Microsoft ticket and any updates/resolutions I'll return here for future reference.


    Thursday, September 19, 2019 1:11 PM
  • Hi,

    Thanks for your posting here and sharing the resolution!

    If there is anything else we can do for you, please feel free to post in the forum.

    Best Regards,


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    Tuesday, September 24, 2019 1:37 AM