This post will be updated in sync with /r/Minecraft's FAQ Thread. Please do not ask for support in this thread; open a new thread or use #minecrafthelp IRC Chat for live support.
As always, downgrading is not, was never and will never be officially supported! Please do not run 1.12 worlds in older versions of Minecraft.
2. Known Incompatible Software
Some software is known to break Minecraft. If your Minecraft stops working, check this list of known incompatible software and see if you have any of those installed. If you do, those software will need to be uninstalled.
One particular offender is ByteFence. If you are seeing an error message like this, it's most likely ByteFence which should be removed from your system. (Bug Report Here)
Error details: Attempting to move successful download to C:/Users\User\AppData\Roaming\.minecraft\assets\objects\somethingsomethingsomething
The process cannot access the file because it is being used by another process
3. System Requirements
Starting from 1.12, Minecraft will no longer support Java 6 or 7. If you are using the latest launcher, you do not need to worry about this as Minecraft ships with its own version of Java. If you know you are using your own version of Java however, you'll need to make sure you're using Java 8.
The OpenGL requirement for 1.12 stays at OpenGL 1.3 (according to internal sources). Please report back if you have a OpenGL 1.3 only system that refuses to run Minecraft even at very low graphics settings.
Hardware requirements for 1.12 is currently staying the same as 1.11, but this may change in the future.
4. Graphics Glitching For No Reason After Upgrading
If your graphics suddenly started glitching since upgrading to 1.12, chances are that your graphics drivers are out of date.
Make sure you have the latest drivers installed and set VBO and VSync to On and set Mipmap to 0 in Video Settings (Options -> Video Settings -> Use VSync/Use VBO -> On).
If you are on a laptop with switchable graphics, you may also want to check that your computer is indeed using the dedicated graphics card.
Since 1.12, /give and /replaceitem no longer bypass item-stacking restrictions and will fail if you attempt to do so. This is to prevent performance issues and bugs. Bug report here
I think it's pretty bad advice to suggest that players should "simply" uninstall a virus scanner when it gives them problems with Minecraft. What's going to keep their computers secured?
There's also no need for such drastic actions: most modern anti virus software provides a whitelist these days. Simply add the Minecraft launcher or, if that doesn't work, add the whole program (launcher) and/or gamedirectory (.minecraft) to the whitelist. After that the scanner won't mess with the game anymore.
I think that's a much more sensible suggestion than just advising people to uninstall the anti virus software, especially considering all the recent ransomware attacks happening.
also most of these "unsupported" anti-v are paid and you can't just uninstall and say nothing happens, go to the forums of your antivirus vendor if you have issues, they will help you, specially if it's paid
This post will be updated in sync with /r/Minecraft's FAQ Thread. Please do not ask for support in this thread; open a new thread or use #minecrafthelp IRC Chat for live support.
You can find the changelog for 1.12 here.
1. Downgrading
As always, downgrading is not, was never and will never be officially supported! Please do not run 1.12 worlds in older versions of Minecraft.
2. Known Incompatible Software
Some software is known to break Minecraft. If your Minecraft stops working, check this list of known incompatible software and see if you have any of those installed. If you do, those software will need to be uninstalled.
One particular offender is ByteFence. If you are seeing an error message like this, it's most likely ByteFence which should be removed from your system. (Bug Report Here)
3. System Requirements
Starting from 1.12, Minecraft will no longer support Java 6 or 7. If you are using the latest launcher, you do not need to worry about this as Minecraft ships with its own version of Java. If you know you are using your own version of Java however, you'll need to make sure you're using Java 8.
You can get Java 8 for all supported platforms here.
The OpenGL requirement for 1.12 stays at OpenGL 1.3 (according to internal sources). Please report back if you have a OpenGL 1.3 only system that refuses to run Minecraft even at very low graphics settings.
Hardware requirements for 1.12 is currently staying the same as 1.11, but this may change in the future.
4. Graphics Glitching For No Reason After Upgrading
If your graphics suddenly started glitching since upgrading to 1.12, chances are that your graphics drivers are out of date.
Make sure you have the latest drivers installed and set VBO and VSync to On and set Mipmap to 0 in Video Settings (Options -> Video Settings -> Use VSync/Use VBO -> On).
If you are on a laptop with switchable graphics, you may also want to check that your computer is indeed using the dedicated graphics card.
Nvidia Optimus Instructions
AMD Switchable Graphics Instructions
5. /give and /replaceitem Behaviour Change
Since 1.12, /give and /replaceitem no longer bypass item-stacking restrictions and will fail if you attempt to do so. This is to prevent performance issues and bugs. Bug report here
#minecrafthelp Channel Manager
<@Notch> whoa, rude language, behave
<@LG_Legacy> Oh relax notch, I'm never serious >_>
<@Notch> I DON'T CARE!!
@Notch runs away, crying
<@LG_Legacy> I made god cry? o_O"
ByteFence i think is more like a virus and not an anti virus. You can use AVG and avast
Subscribe to my channel mixedmegamings,have fun,believe in yourself and may you accomplish your goals.
also most of these "unsupported" anti-v are paid and you can't just uninstall and say nothing happens, go to the forums of your antivirus vendor if you have issues, they will help you, specially if it's paid