User is not showing to me online in COMET chat system

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VB

ASP.NET4

Here I'm using COMET for chatting system but I get problem, when I want to get a online friend where the friend is already online.
I use this code for when user log in the COMET and that user have unique public token and private token no.

Dim manager As CometClientManager = ChatChannelHandler.ClientManager
       'log in if not already logged
       If Not manager.ClientExists(publicToken) Then
           manager.InitializeClient(publicToken, privateToken)
       End If

And get info about who online for that I use this below code
'Here the check friend is online of not

If manager.GetClientByPublicToken(strFriendId) IsNot Nothing Then

''add list of friend if online

End if

Thanks and Regards.

*** Update ***
Suppose A and B is friend. A and B is online. when A is open a chat window it showing his friend B. after I refresh a A chat window it sometime show B on line and some time it show offline. Where the B is already online. so why B user showing sometime online and some time offline.