I had an Outlook 2010 client today that would crash every time the user tried to send an email, click Check Names (ctrl-K), or update the offline address book. Sending or checking names would generate the typical Windows 7 error message saying, “Microsoft Outlook 2010 has stopped working. Windows can check online for a solution…” Attempting to download the offline address book just caused Outlook to stop responding.

The solution was to start Outlook with the CleanAutocompleteCache switch: