The most likely source of your problem is that the Block Scheme or Theme
switching check box has been checked. If you also cannot switch Quick Style
sets (e.g., from Word 2007 to Word 2003), the Block Quick Style Set switching
check box may also have been checked.
Do the following:
On the Home tab, in the Styles group, click the Styles Dialog Box Launcher
(arrow to the right of "Styles" at the bottom of the Styles group) to display
the Styles task pane (or press CTRL+ALT+SHIFT+S)
Click Manage Styles (3rd command button at bottom of Styles task pane) to
display the Manage Styles dialog box
Click the Restrict tab
Clear the Block Scheme or Theme switching check box
(If the Block Quick Style Set switching check box is checked, you'll want to
clear this as well so that you can switch to the Word 2003 Quick Style set)
Leave the default Only in this document radio button checked or click the
New documents based on this template radio button if this is a recurrent
problem (due to a setting in the attached document template)
Click OK
