One thing you can do is find that word in that should not be correct in the dictionary and remove it.
n Word 2007:
1.Click the round Office button in the upper-left corner of the window.
2.Click the Word Options button.
3.Click Proofing.
4.Select CUSTOM.DIC. Be careful not to clear the checkbox.
5.Click the Edit Word List button.
6.Find and select the word you want to delete.
7.Click the Delete button.
8.Repeat steps 6 and 7 as needed.
9.OK out of everything.
Or try this:
1. Verify settings in Word 2007:
a. Open the document that has this problem. Press Ctrl+A to
select all of the text.
b. Click on Review tab | Proofing: Set Language | <choose your
language> | uncheck the "Detect language automatically" and "Do
not check spelling or grammar" boxes | Default | OK.
c. Click on Office Button | Word Options | Proofing | check the
"Check spelling as you type" and "Check grammar with spelling"
boxes | uncheck the "Hide spelling errors in this document only"
and "Hide grammar errors in this document only" boxes | OK.
2. If the previous suggestion doesn't help, then in Word 2007
click on Office Button | Word Options | Add-Ins | Manage:
Disabled Items. If you see any disabled items that relate to
spelling, try enabling them.
3. If the previous two suggestions don't help, then:
a. Close Word.
b. Start regedit. In your Windows registry, if the key
"HKEY_CURRENT_USER\Software\Microsoft\Shared Tools\Proofing
Tools\1.0\Override" exists, delete it.
c. Restart your computer.
And see this link:
http://sbarnhill.mvps.org/WordFAQs/MasterSpellCheck.htm