Error C2664: MessageBoxW cannot convert argument 2 from 'const char ' to 'LPCWSTR'

I keep getting this error message:

State Error C2664 -- int MessageBoxW(HWND,LPCWSTR,LPCWSTR,UINT)': cannot convert argument 2 from 'const char *' to 'LPCWSTR' " 31

This is my code below. I understand it has to do with passing a const type through the what() function in the error class. For some reason it's incompatible. Any ideas?

// on startup execute to determine exceptions
try
{
    // instantiate object app of class AppWindow
    AppWindow app;

    // if(initialize function in class app is executed, and while the app is running, broadcast app)
    if (app.init())
    {
        while (app.isRun())
        {
            app.broadcast();
        }
    }
}

// if the following error is found, execute MessageBox function with following parameters
catch (const std::runtime_error& error)
{
    // parameters(has no owner window so displays independently)
    MessageBox(nullptr,  error.what(), L"An error has occured", MB_OK);
}

return 0;