Error after upgrading to Build 12

I had this error after I upgrade to Build 12 can anyone advise

XML Parsing Error: not well-formed
Location: http://XXX.XXX.XXX.XXX:8787/
Line Number 1, Column 2<%@ Page language='c#' Codebehind='default.aspx.cs' AutoEventWireup='True' Inherits='HostingController.login'%>

8 to Infinity Pte Ltd
Singapore Web Hosting
Established since 1997

Please update your machine with latest XML version to fix this problem.

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