Playing specific custom maps that need mc 1.7.2, and trying to use a mod with forge, but am failing.

I'm using forge version, the recommended version for 1.7.2. Download and run the installer, which reports successful installation. I start MC and select the forge profile and try to run the game, and then nothing. The MC launcher just closes. No errors, no crash reports. It just instantly closes.

Using win7, latest Java version, a brand new Minecraft install with NO mods yet installed.

closed as off-topic by Frank, SevenSidedDie, GodEmperorDune, Robotnik, DJ Pirtu Apr 21 '16 at 5:44

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  • Try using Java 7 (can be installed alongside java 8) or this compatibility patch for Forge. Older versions of forge have a bug that causes them to crash with Java 8 update 20 or higher. Report back if this works, and I'll make it an answer. – MrLemon Mar 11 '15 at 10:23
  • The compatibility patch worked perfectly. Thanks so much. – QuestionableMeat Mar 11 '15 at 14:15
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    I'm voting to close this question as off-topic because it is about tech support for modded Minecraft. We only provide tech support for vanilla Minecraft. – Frank Apr 21 '16 at 3:00

Older versions of Forge have a bug that causes Minecraft to crash on startup if you are using Java 8 Update 20 or newer. While this has been fixed in later versions of Forge, it still affects all versions for Minecraft 1.6.4 and 1.7.2, as well as many versions for 1.7.10.

One solution is to simply install Java 7 alongside Java 8 and correspondingly setting the correct Java path in the Profile Settings in the Minecraft Launcher. You can still use Java 8 for everything else.

Alternatively, Minecraft Forum User FyberOptic has created a patch for older Forge Versions that fixes the issue, by replacing the faulty class file inside the .jar file. Download links for the patched classes for 1.6.4, 1.7.2 and 1.7.10 can be found in the linked thread, along with a description on how use them.

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