It getting Error 13 because it can't find the loginID because it's doesn't work inside a master page.

This will work

<input name="x_login" type="hidden" id="x_login" value="76zggAY2M" />

This will not work.
<input name="ctl00$ContentPlaceHolder1$x_login" type="hidden" id="ctl00_ContentPlaceHolder1_x_login" value="76zggAY2M" />