A new article is now available on www.marifah.net. The Imam discusses the different kinds of bid'a and explains what rulings they carry. Please have a read.
Update: Further to the second footnote in the article, I would like to add that the line كل ضلالة في النار is also not found in hadith #28 of any edition of Al-Arba'een An-Nawawiyyah, with the exception of maybe two. As for the notable translation into English by Sidi Abdassamad Clarke, known as The Complete Forty Hadith and published by Taha, which includes the abovementioned line, I have discussed the matter with my brother Abdassamad and he has stated the following on his blog. Please have a read.
UPDATE (18/03/2017): The marifah.net website is down. The translation is now available here.