VS2013 not connected to tfs,tf31002 record

Before vs2013 connection good, yesterday found no, similar to the following error

Possible Causes and solutions:

1:c:\windows\microsoft.net\framework\v2.0.50727\config under the Machine.config file has garbled problem.
Modified into <? XML version= "1.0" encoding= "UTF-8"?>

2: There is a firewall blocking or other security software blocking the issue.

3:ie proxy settings, I am this problem, because my IE set up the agent, cause can not connect Tfs,tfs yonder have IP filter.

Mine is also the problem, because the use of Cisco VPN client will automatically set up the agent in IE, causing TFS connection is not on.

VS2013 not connected to tfs,tf31002 record