Error working with Lua modules using LuaBridge and C++

Question

I am unable to include a Lua file in another Lua file. I am compiling Lua using C++ and LuaBridge. Here is my main function. Very very small.

    lua_State* luaState = luaL_newstate();
    luaL_openlibs(luaState);
    luaL_dofile(luaState, "res/script.lua");

    LuaRef mainFunction = luabridge::getGlobal("start", luaState);

    try {
        mainFunction();
    } catch (const luabridge::LuaException& e) {
        std::cout << e.what();
    }

    lua_close(luaState);
    std::cin.get();

Here is my "script.lua" file:

mymathmodule = require("mymath")

main = function()
end

And the "mymath.lua" which is in the SAME directory.

mymath =  {
    add = function(a, b)
        return a + b
    end
}

return mymath

The program just crashes. Just removing the "mymathmodule = require("mymath")" line gives no error. What is the problem here??