The problem is that the SessionAccessServlet is returning a response body that looks something like:

1:-123456789:987654321

but is not setting the Content-Type header on the response.

The browser then assumes the default content type, which is text/html, and tries to parse the response as HTML. This fails because the body is not HTML. This is not causing any functional issues, but it is an easy fix and will get rid of the cryptic errors in the error console. To fix, we just need to set the Content-Type header to text/plain, which is the correct mime type for the content.