Hi Balajia,
I found my problem. With the new API 5.1 there is a new feature using ipscope. In API 1.5.1 a network had only one ipscope. Now with the API 5.1 a network have a list of ipscopes.
<Configuration>
<IpScopes>
<IpScope/>
<IpScope/>
<IpScope/>
<IpScopes>
</Configuration>
Seek in your sdk documentation and you will find for the Configuration object 2 methods. One to create an ipscope object and one to create an ipscopes (with a s at the end) . This is the last one you have to use to resolve your problem and after that you have to had your ipscope in the ipscopes. I don't understand why they kept the possibility to had an ipscope object (the one without s) in the configuration object because it does not work or works wrongly.
I hope that will help you,
regards,
Yann