This issue is related to a conflict with WebRoot Secure Anywhere.
Open Secure Anywhere > Identity and Privacy > View/Edit Protected Applications > Switch your external keyboard processes to Allow.
Otherwise, you can disable or deactivate Webroot entirely to get the keyboard working.
If you don't have Webroot installed, check that your operating system language is set to one of the posted supported languages.
English (App Store) or English, French, Italian, German, and Spanish (Steam).
Go to System Preferences/Languages and Regions to check your OSX language setting.
If you've completed these steps and are still running into this problem, please open a support ticket with us.