Probably very delayed, but I've been looking into this and have the answer
You need to ensure the SalesLogix Address Book has been added to Outlook, and logged into SalesLogix
- Tools, Account Settings, Address Books
Outlook 2010 (32bit):
- File, Account Settings, Account Settings, Address Books
If "SalesLogix Address Book" isn't listed, choose New, Additional Address Books, SalesLogix Address Book
If "SalesLogix Address Book" is listed, select it and choose Change
Fill in the username/password/connection, or select "Prompt on Startup", restart Outlook, and you should have the Go To SLX button available again!