Hey Deepak,
We’re still trying to track down some details about what may be going on here. If you downgrade to a previous version of the plugin which uses an API Key instead of Oauth (a version before 1.3, from here), does the problem persist for you or does it function normally?
Can you possibly email us with a few extra details? The details we’d like to get from you:
1) Your login username and the account (if different) connected to the plugin.
2) The URL of the site you’re integrating this plugin with.
If you can send those to us at wordpress [at] mailchimp [dot] com, We’d like to take a deeper look to see if we can see the source of the problem there.
We’ll continue communicating with you here through the forum, so if you could shoot us that email with details as well as reply concerning trying an older version of the plugin, we’ll get back to you here.
Thanks!
Gabe