I have a big problem. I created a modpack 1.7.10 and wanted to create a server with that modpack to play with my friends. Then start the minecraft client with the mods and open normally. But then when I launch the launcher and try to enter server whith localhost, I do not have to go in and I get this error. I've tried a lot to solve the problem but nothing.Exactly when I click on "join server", it do this error and the screen with me is displayed: "Fatally missing block and items"
OK, I did some google searches and found it could be two problems, one being that the mods or configs are different between the server and the client, but I would think you have both configured exactly the same? Be sure they are.
The other problem could be your operating system is running in a different language and is transferring that setting to Minecraft, and it is then causing errors because it can't match the internal names of items with what is displayed on the screen. See this post: