I have had luck by just copying the old Stream_AutoComplete_XXX dat file from C:\Users\username\AppData\Local\Microsoft\Outlook\RoamCache folder and renaming it to whatever the new dat file is.
Course you can try:
- Click Start, and then click Run.
- In the Open box, type outlook.exe /importnk2, and then click OK. This should import the .nk2 file into the Outlook 2010 profile.
Note After you import the .nk2 file, the contents of the file are merged into the existing nickname cache that is currently stored in your mailbox.
Or try the FIX IT for me solution provided by Microsoft. That’s worked once or twice too.