Your template contains unsafe Twig tags, functions or globals. Please check it and remove any of these code constructs: block, set, embed, macro, filter, apply, verbatim, sandbox, with, include, import, from, use, extends, do, flush, passthru, exec, eval, system, shell_exec, proc_open, popen, assert, file_put_contents, file_get_contents, unlink, fopen, fwrite, call_user_func, call_user_func_array, create_function, _self, _charset, _env, globals. Also make sure you do not use string concatenations inside functions or filters calls.