<configuration>
<connectionstrings>
<<big>add name="ConString"</big> ConnectionString="Data Source=xxxxxx;Initial Catalog=WPFTraining;Persist Security Info=True; providerName="System.Data.SqlClient" name="ConString"/>
</connectionstrings>
</configuration>
for windows authentication
<configuration>
<connectionstrings>
<add ConnectionString="Data Source=xxxxxx;Initial Catalog=WPFTraining;User ID=xxxxxx;Password=xxxxxx/>
</connectionstrings>
</configuration>
for sql server authentication
..try this