Common issues and fixes

[Semisol]

ClassNotFoundException: sun.misc.ObjectInputFilter

This means you are using an outdated Java 8 version. Please change the Java install from your launcher you use to something newer than 1.8.0_51.

InvalidClassException: filter status: REJECTED

This means that one of your mods got caught by the filter or there's an attempted attack against you. Depending on the case:

If you are playing singleplayer

Please launch your game with the option -Dinfo.mmpa.pipeblocker.log-only=true, play a little bit on singleplayer, and send your latest.log on a new issue. Remove the option after you have done so, as it disables protections.

If you are playing multiplayer

Please send your latest.log, and please repeat the steps in the singleplayer section in a singleplayer world (as it requires disabling protections) and send the log from that too.

Unable to read a class file correctly

This is something you can safely ignore, and is impossible to prevent due to how Forge works.