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After pressing the log in button it would said updating minecraft and after that it said Failed to launch
Fatal error occurred (4): null
I have forced an update and updated Java but it still doesn't work. Not even the demo works.

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marked as duplicate by galacticninja, Robotnik, 5pike, Studoku, Mathias711 May 28 '15 at 10:47

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

It's possible that something may be blocking the download. Take a look at your firewall settings and see if that's the problem. – Coronus Mar 11 '13 at 22:08
Is this a fresh install, or one that worked previously? – Coronus Mar 11 '13 at 22:09

It's likely your antivirus/firewall. Apparently Avira 2012 and McAfee have been known to prevent the connection to Minecraft update servers.

Here is one such report

If you're comfortable doing this, you could try temporarily disabling your antivirus while Minecraft updates.

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I had this problem before, and I had to delete my minecraft.jar to get there.

For Windows: Win + R. Then inside the text box type %appdata%. Go to your .minecraft folder and find your bin folder, and inside of that delete minecraft.jar. Then open the Minecraft launcher and click "options", then click "Force Update". Then log in to Minecraft, and done.

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