The latest updates to MAC OSX (10.9.5) have caused issues with the Citrix receiver where a user is unable to type when after they log into the Citrix or Deskscaler session. To resolve the issue the user needs to switch focus to the OSX Desktop and change focus back to the Citrix session and they keyboard commands should work. To change focus to the OSX desktop use cmd -tab.
If this does not work try installing the latest Citrix receiver from http://www.citrix.com/downloads/citrix-receiver/mac.html and try again.
Further information on this issue is available at: https://discussions.apple.com/thread/6544096