EPM 10 ADD IN error

Hi !

I am able to install epm 10 add in for excel . I am facing  below error while creating connection.

Unable to deserialize XML body with root name 'html' and root namespace '' (for operation 'Logon' and contract ('ISessionService',  'http://tempuri.org/')) using XmlSerializer. Ensure that the type corresponding to the XML is added to the known types collection of the service.

Please help ...