This error means that another extension, plugin or template on your site is including Facebook's deprecated all.js Javascript library. That is the 'old' version of the Facebook Javascript API which was discontinued. It's no longer meant to be used and can cause conflicts with some JFBConnect features, as JFBConnect uses the recommended sdk.js library. Some common extensions that included Facebook features are JomSocial, EasySocial, K2. You will need to check your plugins, components and/or template for any Facebook features and try to disable them.
Since you specifically mention JomSocial, please go into the Integrations section of JomSocial and make sure that you're have the 'Use SourceCoast's JFBC' setting enabled. If that doesn't solve it, you'll need to continue to narrow down the problem by going one-by-one through your extensions.
-Melissa
Jomsocial register and login with Facebook button not working
