This error usually happens when you are logged out of your Facebook account.
It can also be caused by you not having permission to publish to the page with the account you're currently logged into.
Common Error 100 Messages
(#100) Length of param name must be less than or equal to 255
(#100) The parameter name is required
The Fix
Make sure you're logged into the correct account — the one that is an admin of your Group or Page.
If you are logged in correctly, reach out to the Page or Group admin to make sure your permissions are set to Moderator or above.