When you click New Message from the top right hand corner and the new message form appears, the Recipients entry must have an exact User name in it. For example, if you type Kishore, E2E will find that User. You can then click the Username in the search results box and E2E will add that Username to the Recipients field.
If you go to you list of Friends and click Connect beneath the Username you wish to send a private message to a popup will appear with three items in it, Send Private Message, Email Subscribe to User, Unfriend. Select Send Private Message and the new message window will appear with the Recipient field populated with the Username that you've chosen.
I'm not sure what's happening with the Error you describe, as I was able to send you a PM as you described without receiving an error.
If the issues persist, make sure the browser you're using is up to date and try clearing the cache and restarting.