WPF application db connection not open in some Machine why?

See more:

SQL

WPF

SQL-Server-2012

, +

Dear all,
I have a WPF application and its db is SQL server 2012. Im Using .edmx file to get model (Db first approach).
This is done in a separate project in my solution. Im using VS2012.
My connection string is some thing look like in my app.config

<add name="DigitizationEntities"
          connectionString="
          metadata=res://*/Model.DigitizationModel.csdl|
                   res://*/Model.DigitizationModel.ssdl|
                   res://*/Model.DigitizationModel.msl;
                   provider=System.Data.SqlClient;provider connection string="data source=XXX\SQL2012;initial catalog=DBDigi2015;user id=sa;password=MyPassword;MultipleActiveResultSets=True;App=EntityFramework"" providerName="System.Data.EntityClient" />

some machine with windows8,windows8.1,and 7 are working fine. but some machine not getting the connection and the error "underlying provider failed on open" is showing.

i am using entity framework version 6 for the same.

i also tested with new virtual machine and installed pc but its not getting.firewall is off.
why this happening? am i miss any dlls? or need to install any framework?
is any network issue or configuration problem??

Thank you!!.