We've had an issue where the CRM buttons were greyed out in Outlook 2010 and CRM 2011. The Outlook CRM addin was properly installed and enabled but when the user opened Outlook and selected the CRM tab, all CRM related buttons and actions are greyed out. This happened when Office 2013 (or later) component was installed on the user’s PC. Because there are shared components between versions, it created an incompatibility.
As a first step, check event viewer to see if there are any application errors that have been logged regarding the MSCRMAddin load behaviour.