[1.7.10] Setting up a variable in a message send when pressing a button

Hi I'm trying to set up some code that when a GUI button is clicked it sends a command that takes a variable from what button is pressed and inserts into the command.

Minecraft.getMinecraft().thePlayer.sendChatMessage("/" + classe + "");

the

classe

is already defined and working in the rest of the mod, however when pressed, I am kicked and it pops up "Illegal characters in chat". What am I doing wrong? Thanks for any help.