Question : "Messaging Interface Returned an Unknown Error" when composing message

I have a client who has Outlook XP, Windows XP SP 2 running on a Sony Vaio laptop.  All of the updates for both Office and Windows are current and installed.  She is also running Norton Protection Center.

When my client starts a new message, she clicks on the "To" button to access her Personal Address Book.

She gets the dreaded "The messaging interface has returned an unknown error" message.

I have built a new profile, pointing to the same address book.  Same result.

I have tried deleting the address book, having Outlook build a new one, same result.

I have tried copying the address book, using the copy, same result.

I am ready to re-install Outlook if necessary.

I have Googled my butt off for two days trying to find someone who has gotten that error for this reason.  Nothing.

The ONLY way I can get the problem to go away TEMPORARILY is to delete the Personal Address Book, then re-add it, then restart Outlook.  Problem is, after I restart Outlook the second time, the problem comes right back.

Please advise.

Answer : "Messaging Interface Returned an Unknown Error" when composing message

Greetings, geofflilley !

To autocomplete feature of Outlook is compose of the address book and nickname file. The nickname file may be corrupt. The names are kept in a NK2 file.  With Outlook close, search for *.NK2 and rename the file.  When Outlook opens, a new one should be created.

.NK2 file is located in
C:\Documents and Settings\\Application Data\Microsoft\Outlook folder. It is a hidden file. Go to any folder and select Tools > Folders Options > View. Check "Show hidden files and folders".  Click OK.


Best wishes!