Facebook permission issues can sometimes be fixed by removing Ecamm from your Facebook account and then re-adding it. This process will not remove any posts or change the content on your business Pages or Profile.
To do this, follow these steps:
Go to Facebook, and ensure that you have picked your personal profile in the top-right corner menu.
Once you've picked your personal profile, go here: http://facebook.com/settings?tab=business_tools
Remove Ecamm for Mac from the list of business integrations by clicking the blue Remove button.
Once it has been removed, quit and re-open Ecamm on your Mac. When it re-opens, you should see a message that Facebook needs to be re-authorized. Follow the prompts to give Ecamm permission to post.