So you open up F12 and see this obscure error:
In some cases this is caused by browser updates or perhaps server changes like adding gzip support to IIS.
This error in most cases is to to some code not properly closing before another script is executed thus chunking the response.
You should review the code for the page and look for Response.Close(); method. Something like this:
and replace it with a proper Response.End(); method instead.
Now save and reload your page.