Minecraft command too long
One command cannot be to long for a command block. It is possible that two or more commands are needed for what you are trying to accomplish.
Another possibility is you are trying to type it in the chat by just pressing T for talk. commands in chat are restricted to a certain length and therefor cannot run all commands through the chat if to long.
Try giving yourself a command block by typing /give <name> minecraft:command_block then copy and paste the command you want to run.