1. Sins which May or May not fall into disbelief!

2. Following groups and sects that go against the Sunnah
Abu Dawood, ad-Daarami, Ahmad, al-Haakim and others narrate that Mu'awiyah ibn Abi Sufyan said:
"The Messenger of Allah stood up among us and said: "There were some among the People of the Book before you who divided into seventy-two sects. This nation will divide into seventy-three sects, seventy-two of whom will be doomed to the HellFire, and only one in Paradise. (This group) is al- Jamaa'ah"

3. How to understand this Hadith:
Those who call themselves Muslims yet they adopt rules that made them a separate, independent group and caused them to abandon many texts of the Qur'an and Sunnah fall into this category. Examples are:
The Khawaarij The Mu'tazilah The Rawaafidh The Terrorist groups of Today
Also those sects that show faith but conceal hatred in their hearts will be damned to eternal hell such as:
The Ismaalis The Druyze The Nusayris The Baatinis
As for those who adopt the Qur'an and Sunnah and do not deviate from them, if they differ in some matter it does not mean that they are counted as one of the (doomed) sects.

4. Refusing to Migrate for the Sake of Allah
Muslims are not permitted to remain in Lands of which they are not allowed to practice their religion openly; or lands in which the fitnah is so great and they are too weak to resist it. If faced with these two things, one should move to another part of the land in which they can practice their religion or not fall into the temptation if it is too great for them. Allah Says:
"When the angels take the souls of those who die in sin against their souls, they say: "In what [plight] were you?" They reply, "Weak and oppressed were we in the earth". They [the angels] say: "Was not the earth of Allah spacious enough for you to move yourselves away from evil?" Such men will find their abode in Hell - what an evil refuge [or destination]! Except those who are really weak and oppressed - men, women and children, who have no means in their power, nor [a guide post] to direct their way". (4:97-98)
So thus Migrating becomes an obligation unless one had no means to do so

5. Judging Unjustly
Allah revealed His laws to establish justice among mankind, and He commanded His slaves to be Just:
"Verily Allah commands the justice [and] the doing of good.." (16:90)
He has made it obligatory for rulers and judges to be just and never to be unfair:
"Allah commands you to render back your trusts to those to whom they are due; and when you judge between man and man, that you judge with justice". (4:58)
The Prophet said,
"There are three types of judges: one will be in Paradise and the other two in Hell. The one who will be in Paradise is the one who knows the truth and judges according to it. As for the one who knows the truth but is unjust in his judgement, he will be in Hell, as will the one who judges between people without understanding or knowledge". (Abu Dawood]

6. How to Understand this Hadith:
Too many are the Muslims of today who have made themselves to be Judges over others. People come with questions about Islam and they issue fatwa (Answers) when they are not qualified to do so. Not only do they fall victim to the bad mentioned in the hadith but also they commit the sin of “speaking about the Deen without knowledge” which is a form of Association of Partners to Allah.
Allah says that among the things he hates the most includes:
"and saying things about Allah of which you have no knowledge. " [Al-A'araaf 7: 331
The Prophet said: “Verily, Allah does not take away knowledge by snatching it from the people but He takes away knowledge by taking away the scholars, so that when He leaves no learned person, people turn to ignorant as their, leaders; then they are asked to deliver religious verdicts and they deliver them without knowledge, they go astray, and lead others astray.”
So we must beware of this as Muslim's today. Leave the Fatwa to the bonafide Qualified Scholars!

7. Lying about [ by falsely attributing words to] the Messenger of Allah (saw)
Whenever one says that the Prophet said or did something he did not say or do; or whenever a person mis-interprets the meaning of a Hadith, he or she has lied on the Prophet and such a sin can land a person a seat in hell forever.
The Prophet told Ali: "Do not lie about me (or falsely attribute anything to me) for whoever lies about me will enter Hell".
Bukhaari reported that Salaman ibn al-Akwa' said: "I heard the Messenger of Allah (saw) say: "Whoever attributes to me words that I did not say, let him take his place in Hell".
Also the Prophet said: "Lying about me is not like lying about anybody else. Whoever lies about me, let him take his place in Hell".
Again – we have to be careful putting ourselves in the shoes of a scholar when we are not qualified to do so. Leave the teachings to those who are qualified to teach!

8. Outer Pride (Arrogance)
Inner pride is prase-worthy and needed to be a true believer. But the outer Pride is what is unlawful and a form of Disbelief. The Prophet said that Allah said, "Pride is My cloak and greatness is My robe. Whoever competes with Me in respect of either of them, I shall admit him to Hellfire".
Ibn Mas'ud said: "The Messenger of Allah (saw) said, "No one who has an atom's weight of pride in his heart will enter Paradise". A man said, "But what if a man likes his clothes and shoes to look good?" He said, "Allah is beautiful and loves beauty. Pride is rejecting the truth and looking down on people". (Muslim).
So thus to take pride in one's appearance, or self is a good thing. However when one thinks himself to be better than others – this is the pride that will condemn one to the hell fire forever!

9. TO BE CONTINUED!