The {JFBCSubscribe ..} tag was removed a few versions back in JFBConnect. It's been replaced with the {JFBCFollow ..} tag. All the parameters are the same, but Facebook changed the name on it and we needed to update our tag as well.
You'll need to find out what is adding the tag to the bottom of your page and update it:
* (Likely) If you have an instance of the JFBCSubscribe module created for that position, you'll want to disable it and create a new SCSocialWidget module there instead. Use the Facebook -> Follow widget inside that module and configure however you need.
* (Unlikely) If you added the {JFBCSubscribe} tag to your template or an article, you'll need to update the tag in that article to {JFBCFollow}
I hope that helps explain, but if not, or you have any other questions, just let me know.
Thanks,
Alex