I tried to join Mineplex today, and my Minecraft was just stuck on a blank screen when I tried. Anyway, I forced it to close and looked at the log. Here is the error that I found:
[10:28:38] [Netty Client IO #7/INFO] [FML]: Unexpected packet during modded negotiation - assuming vanilla or keepalives : net.minecraft.network.play.server.S46PacketSetCompressionLevel
[10:28:38] [Netty Client IO #7/INFO] [FML]: Aborting client handshake "VANILLA"
[10:28:38] [Netty Client IO #7/INFO] [FML]: [Netty Client IO #7] Client side vanilla connection established
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: java.lang.NullPointerException
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at eu.crushedpixel.replaymod.recording.PacketListener.handleResourcePack(PacketListener.java:150)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at eu.crushedpixel.replaymod.recording.PacketListener.channelRead(PacketListener.java:103)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher.channelRead0(NetworkDispatcher.java:249)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraftforge.fml.common.network.handshake.NetworkDispatcher.channelRead0(NetworkDispatcher.java:50)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:103)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:153)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:153)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:153)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.handler.timeout.ReadTimeoutHandler.channelRead(ReadTimeoutHandler.java:149)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:338)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:324)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:785)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:132)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:485)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:452)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:346)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101)
[10:28:38] [Netty Client IO #7/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.Thread.run(Thread.java:745)
