Problem: Connecting to servers say "Internal Exception: java.lang.NoClassDefFoundError: net/minecraftforge/fml/common/registry/GameData" and fails to connect.
Other probable, existing parameters:
OptiFine_1.12_HD_U_C4 (in mods folder)
Mostly any form of Minecraft forge 1.12 will be either not recognizable by Minecraft's launcher causing it to launch in failure or crash during the Mojang mod loading screen with Replay Mod installed; some work and get through the mod loading screen but fails to connect to any server containing the error above
Java(TM) Platform SE binary and the Minecraft Launcher are both ran in High-Performance NVIDIA processor
My rig: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60Hz 2.60GHz; 8.00 GB RAM (7.83 usable); 64-bit Operating System, x64-based processor; Touch Support with 10 Touch Points; GeForce GTX 960M; Driver version 384.76
I am also experiencing this issue, and I am also unable to download anything from the replay center. I noticed that the folder "/fml" does not exist.
I found a fix!! Use the mirror, because the main link actually is incorrect and is the same as the "Replay Mod v1.12-2.0.0-b7", instead of "Replay Mod v1.12-2.0.0". Use THAT with forge, and it should work perfectly.