Computers not reporting to WSUS server

Dear experts,

I'm building a SCCM12 Lab to toy with. Infrastructure is:

- 1 CAS
- 1 Primary
- 1 DC

Both the CAS and Primary servers are WSUS/SUP enabled, with the CAS synchronizing with Microsoft while the Primary is synchronizing with the CAS (upstream synch). Databases are SQL Server 2008 R2 Standard.

WSUS settings are deployed through GPO, assigned to all 3 computers, specifying the Primary server as source.

After some initial problems and research I installed http://support.microsoft.com/kb/2720211 on both servers.

I successfully deployed the SCCM 12 Client as an Update on all machines. But that was my only success:

- All computers, when I manually check for updates, will tell me that I am up to date
- All computers still appear as "not yet reported" in the WSUS console on the Primary server.

I've checked the %windir%\WindowsUpdate.log on all machines, and they show this error:checkupdates.txt

I tried to run a wuauclt /resetauthorization /detectnow on all machines, it looks like it works fine, as shown in the log: resetauth.txt

..but the machines will stay as "not yet reported", and the GetCookie error shown in the first log will eventually appear again after some time.

Most of the similar issues I find on the web talk about an Office 2003 update...this doesn't apply in my case.

Any idea what else I could try to troubleshoot the issue?

Thank you in advance.