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I have tried to reinstall Minecraft with Forge multiple times, but Minecraft still won't launch.

When I check "Launcher Visibility" and change it to "Hide Launcher" and re-open, I get this error log in the console:

[13:20:11] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[13:20:11] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[13:20:11] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
[13:20:11] [main/INFO] [FML]: Forge Mod Loader version 7.10.18.1180 for Minecraft 1.7.10 loading
[13:20:11] [main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_20, running on Windows 7:amd64:6.1, installed at C:\Program Files\Java\jre1.8.0_20
[13:20:11] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[13:20:11] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker
[13:20:11] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[13:20:11] [main/ERROR] [LaunchWrapper]: Unable to launch
java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.8.0_20]
    at java.util.ArrayList$Itr.remove(Unknown Source) ~[?:1.8.0_20]
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:117) [launchwrapper-1.9.jar:?]
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.9.jar:?]

How can I resolve this?

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4 Answers 4

Reset to default
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You are not using Forge 10.13.0.1180 as shown on this line

[13:20:11] [main/INFO] [FML]: Forge Mod Loader version 7.10.18.1180 for Minecraft 1.7.10 loading

What i would do is make a copy of your saves and then completely delete the .minecraft folder from appdata.

Reinstall minecraft completely from scratch and then

Use this link to install the correct version of Forge.

It should work fine if you do this

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  • No need to delete .minecraft, that would reset everything (fair warning would be a bit nice) especially all you're looking to do is update Forge.
    – Extreme
    Aug 28, 2014 at 15:07
  • I would delete .minecraft because as long as you back up your saves it will make no difference it just gives a complete fresh start
    – Flaunting
    Aug 28, 2014 at 15:18
  • I've removed the adf.ly link, as we don't allow self-promotion of that sort. I'm assuming it was just a straight copy/paste, but it's a good idea to double-check and sanitize any links you provide.
    – Frank
    Sep 5, 2014 at 21:18
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You don't need to "downgrade" or "uninstall" Java 8 but you do need to have Java 7 on you machine - and you can run it side-by-side with 8.

The steps I took were:

  1. Install Java 7u76 - I went for the x64 .exe - by default it will install to c:\Program Files\java\jre7\ which should be fine, and won't upset Java 8 - but make a note of this location for step 3.
  2. Ensure forge is up to date - at the time of writing I went for 1.7.10-Recommended 10.13.2.1230 - run the updater, choosing "Forge Client" and pointing it at your Minecraft install.
  3. Run the Minecraft Launcher, select the "Forge" profile, and select "Edit Profile", then in the "Java Settings (Advanced)" section, check the box for the executable and change the path to c:\Program Files\java\jre7\javaw.exe and then save the profile:
    Profile Editor Steps
  4. Play!

Remember though that you'll probably have to change this setting next time you update Forge as I think it seems to revert the settings back to their defaults when you run the updater.

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Tip 1: Try down grading Java to Java 7. This is just a fail safe. Forge definitely works with Java 7

Tip 2: Make sure you have launched Minecraft without Forge before trying with Forge. Sometimes this can fix issues with Forge and Minecraft compatibility.

Tip 3: Make sure you are running the correct version of Forge.

There is no need to uninstall Minecraft and re-install.

How To Install Forge for Minecraft 1.7.10

Here is a quick tutorial video I made on installing Forge for Minecraft 1.7.10

  1. Download Forge for 1.7.10 from here
  2. Activate the installer and select "client"
  3. Open Minecraft launcher and select "New Profile" (bottom left)
  4. Name the profile something like "Forge 1.7.10" and select Forge 1.7.10 from the drop down a little further done the profile making page. Save the profile.
  5. Select your new profile and hit "Play"
  6. Enjoy playing modded Minecraft.
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  • Hello, welcome to Arqade. As a rule, we require that you disclose when you reference outside resources that you are affiliated with. In this case, it just means that you have to say in your answer that you made the video you linked to.
    – murgatroid99
    Oct 27, 2014 at 17:34
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You need to get Java 7 because Java 8 is not compatible with Forge, so here's the download page.

Also, configure Java's security to medium.

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  • make sure you configure java security to medium
    – havan1337
    Oct 27, 2014 at 14:55
  • What would setting security to medium solve?
    – JvR
    Feb 2, 2015 at 11:19

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