First check this node. As it states 8 times out of 10 assuming that the cookie has been set correctly (your post suggest that this is so) then problem is with the server IP's. When the server returns to pick up Cookie who it says it is is not he same as who set the cookie. This can happen for various reasons. There are several environment dependent ways to test this. Please give more details about your systems environment if the suggestions in node don't help.

mitd-Made in the Dark
'My favourite colour appears to be grey.'