You can’t enable Use Cached Exchange Mode because it is grayed out.

This is likely because of a Group Policy that is in effect on your computer. If you are on a company network, you might want to contact an administrator to disable it. Otherwise, you can try to enable it yourself.

1. Hold down the Windows key and press R. (Or click Start > Run and type regedit)

2. Type regedit and click OK.

3. Click the plus sign next to HKEY_CURRENT_USER
then Software
then Microsoft
then Office
then 12.0
then Outlook
then click OST

4. Right-click the NoOST entry on the right and click Modify.

5. Give it a value of 0.

6. Restart Outlook 2007 and the Use Exchange Mode option shouldn’t be grayed out anymore.