This error message usually points to the email editor that you are using and is not set properly. Please do the following steps...
- Click Start, click Run, type regedit in the Open box, and then click OK.
- Locate and then click the following registry subkey:
HKEY_CURRENT_USER\Software\Microsoft\Shared Tools\Proofing Tools\Custom Dictionaries
- Set the value of CUSTOM.DIC to 1.
- Exit Registry Editor
Hope this helps~!