guys,
I never face this problem on sify.
I have 3 laptops configured via wireless lan and I can log in from any of them via IP binding(done by sify).
I an log on from laptop 1 and immediately after that log on via lappy 2, no probs. I never get this message.
best option would be to call their service center and have them log you out.
Also check with them how many/ and which mac ids have been usng this connection.