Cookies not working in IE9 on 2008R2

Hi All,

We have a very strange issue where our desktops running Win7 x86 + SP1 and IE9 can successfully access an internal web application that uses cookies. The cookie is used to call up a customer and is retained in the session until you log out the app.

However if I run that same app on 2008R2 + SP1 with IE9 the cookie is expiring after approximately 20 seconds and all the customer information is lost.

- If I re-enter the customer information a 2nd time then the cookie seems to be retained.
- If I open the app in the browser and then open it a 2nd time in a new tab/window the application works fine and the cookie is retained
- I have tired with/without the same IE GPO's that are applied to the desktops to ensure all settings (including the cookie settings) are identical
- I have tried on both IE and IE x64 on the server
- I have a small random selection of other Windows 2008R2 servers where the app works fine without the need for multiple tabs/windows. In theory these servers are identical builds and patch levels and IE versions which makes no sense to me.

I have tried the TabProcGrowth registry key on 0 and 1 but it has not made any difference.

I am pretty stumped on this now...