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Windows Mail Spell Check Language is no longer available for Spell Checking
http://www.vistaarticles.com/articles/346/1/Windows-Mail-Spell-Check-Language-is-no-longer-available-for-Spell-Checking
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Published on 05/6/2007
 
Tip to fix spell check which dosen't work in Windows Mail.

Windows Mail Spell Check Language is no longer available for Spell Checking

When you run Windows Mail for the first time, you may receive the following error:
This language is no longer available for Spell Checking. Please select another in the Spelling Options Dialogue.

To fix:
1. On Windows Mail main window click Tools
2. Options
3. Spelling
4. Choose a language except English
5. Apply
6. Choose English
7. Apply

Should work now.