Last reviewed on March 12, 2012   —  17 Comments

When you receive this error message:

Could not complete the operation. One or more parameter values are not valid.

while addressing or sending an email message, meeting request, or assigning a task, or saving a new contact, your auto-complete list may be corrupt. Some users also report getting this error when they save an appointment or task.

The solution: clear the auto-complete list cache.

Outlook 2010: Clear Names from the Auto-Complete List

To remove single addresses, select the name using the arrow keys then press Delete. In Outlook 2010, you can also click the x beside the name to delete it or use the Backspace key.

Empty Autocomplete cacheIn Outlook 2010, you can clear the cache using the File, Options, Mail dialog, Empty Auto-complete List button.

You can also close Outlook and use the /cleanautocompletecache startup switch. To use, press Windows key + R to open the run command then paste

outlook.exe /cleanautocompletecache

in the Open field and press OK.

Outlook 2007 and Outlook 2003

To remove single addresses from the list in Outlook 2007 or Outlook 2003, select the name using the arrow keys then press Delete.

In Outlook 2007 and Outlook 2003, you can remove all of the addresses from the autocomplete cache, either by deleting the NK2 file (at %USERPROFILE%\Application Data\Microsoft\Outlook ) or by opening Tools, Options, Email Options, Advanced Email Options and deselecting the option to suggest names near the bottom of the dialog.

More Information

For a list of utilities you can use to edit the auto-complete cache, see Understanding Outlook’s Auto-Complete Cache (*.NK2)


  1. Peter Chisnall says

    I am getting this error message when I try to send new emails.

    I carried out the instructions above and cleared the cache but it still doesn't work.

    Any ideas?



  2. Fred says

    Same error but only when replying to all. Cleared the cache but no luck there as the message remains.

    Is there a fix for this?


  3. Doc says

    The only thing that fix this to me, was create an X500 address in all my users, update the cache in the server and update the cache in the client

  4. heha Ha says

    I face this problem today when sync my hotmail a/c on Outlook 2003 with server (MAPI connection). All folders cannot be sync.

    By same Outlook profile, I have another Live email account (also MAPI connection). There is no problem on sync between client side and server.

    When lead to problem and how to solve? Please advise

    • Diane Poremsky says

      Do you get any error messages in Outlook 2003? Look in the sync error folders and see if any of the messages hold clues.

  5. Mark says

    Hi Diane,

    My users get this error when doing a very specific process in Outlook 2010 on Win7.

    Open an email they have received.
    Enter a name in the To: field
    Move the email to another folder.

    Apparently this works in Outlook 2007 but they are running XP (if that makes any difference).

    • Diane Poremsky says

      I don't think the Windows version matters. Are they adding names to the To field of Draft messages or of messages they received?

  6. Mark says

    They are opening a message they have received then entering a name in the To: field. After that they try to move the message to another folder and get the error.

  7. Nelson says

    I have a problem where the tasks do not appear in the To Do Bar. I tried /resettodobar on startup and nothing. Also /resetnavpane with similar results.

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