I couldn't get it working with your code but I got it working with this code,
Code:
Private Sub CommandButton3_Click()
ActiveDocument.Unprotect
ActiveDocument.CheckSpelling
ActiveDocument.CheckGrammar
ActiveDocument.Protect _
Type:=wdAllowOnlyFormFields, _
NoReset:=True, _
Password:=""
End Sub
The only problem is that if you press cancel on the spell checker I get an error message saying "The ToolsProtectDocument is currently disabled".