Unable to make the session state request to the session state server

Our site is currently having this problem. Basically it only happen when we click some particular links where it will pop-up a new window.
This is the error message we receive :

Unable to make the session state request to the session state server.

Please ensure that the ASP.NET State service is started and that
the client and server ports are the same.
If the server is on a
remote machine, please ensure that it accepts remote requests by
checking the value of
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\aspnet_state\Parameters\AllowRemoteConnection.

If the server is on the local machine, and if the before
mentioned registry value does not exist or is set to 0, then the state
server connection string must use either 'localhost' or '127.0.0.1' as
the server name.

target site :
Void
MakeRequest(StateProtocolVerb, System.String, StateProtocolExclusive,
Int32, Int32, Int32, Byte[], Int32, Int32, SessionNDMakeRequestResults
ByRef)

this is the webconfig that contain sessionstate tag :

<sessionState mode="StateServer" timeout="45" />

I have check the ASP.NET State Service, and it is currently started and set to automatic

I have set the registry stated in the error message to 1, but still not working.