One I open page permission tab for any page in my DNN site it will prompt an error message call "Default.aspx?__U=1461820909481:1 Uncaught TypeError: Cannot read property 'value' of null"

and source in "<form><input type="hidden" id="__DNNCAPISCSI" value="200"><input type="hidden" id="__DNNCAPISCSDI" value=""

could you please tell me what is the meaning of

<input type="hidden" id="__DNNCAPISCSDI" value=""> and why it is empty ? what is the value it should contain? Thank you very much