When I tried to use the regular installer as well as the .jar file, I get a log and it reads: 

Exception in thread "main" java.lang.ExceptionInInitializerError
    at net.minecraftforge.installer.ClientInstall.getSponsorMessage(ClientInstall.java:326)
    at net.minecraftforge.installer.InstallerAction.getSponsorMessage(InstallerAction.java:59)
    at net.minecraftforge.installer.InstallerPanel.updateFilePath(InstallerPanel.java:236)
    at net.minecraftforge.installer.InstallerPanel.<init>(InstallerPanel.java:217)
    at net.minecraftforge.installer.SimpleInstaller.launchGui(SimpleInstaller.java:153)
    at net.minecraftforge.installer.SimpleInstaller.main(SimpleInstaller.java:40)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 1
    at net.minecraftforge.installer.MirrorData.buildMirrorList(MirrorData.java:84)
    at net.minecraftforge.installer.MirrorData.<init>(MirrorData.java:63)
    at net.minecraftforge.installer.MirrorData.<clinit>(MirrorData.java:17)
    ... 6 more

 

Can someone help?

I got this same problem, when I looked deeper into forums I noticed that a mod responded to someone with this same question and stated that they are aware of the issue and will solve it "eventually" since older versions are not "supported"

Edited April 20, 20214 yr by TP_Banditz