If you are having problems with the Connect to Outlook icon being disabled or greyed out when using Sharepoint 2013 please try one of these solutions to resolve the issue. You may also receive the following error message:
Error Message: This control is currently disabled. You might not have the right permission level to use this, you might need to select an object or item, or the control might not work on this context.
Option 1. Refresh the Page
Please try refreshing your web browser by hitting F5
Option 2. Temporarily Disable Minimal Download Strategy
Disable the Minimal Download Strategy feature in Sharepoint.
Go to Site Settings, Site Features and Deactivate Minimal Download Strategy
Option 3. Add Sharepoint site to “Trusted Sites” in Internet Explorer
In Internet Explorer settings go to the Security Tab and add the Sharepoint site. Also try lowering the restrictions for the “Trusted Sites” zone.
Option 4. Check Regional Settings and Time Zone in Sharepoint 2013
On the Sharepoint site check that the Regional Settings and Time Zone settings are matching your clients settings.
Option 5. Copy the Web Address Manually and Paste in Your Browser
Go To Calendar, On the calendar tab click “List Settings”
Copy the web address (e.g. http://domain.com/site/Lists/Calendar/calendar.aspx) and paste the URL in your browser, Press Enter
Go to the Calendar tab and Click List Settings and try again.