If you use 4G RAM, Sametime 8.5 and Windows 2003 R2 you can go crazy

Last week we started another new setup of Domino 8.5 and Sametime 8.5 (small company with 12 users).
Now a long history.

We setup Domino 8.5.1 and Sametime 8.5 as usual. Domino works great but Sametime 8.5 not. The users try to logon using sametime client but nothing happens.
The sametime client can't connect to the server. The STPresenceSubscriptionMgr sevice doesn't start.
I try everything i Know, and check everything about Windows.

We reinstall all the environment  and nothing. We setup another windows machine and it works.  

I open an PMR and IBM told us that the problem was with Windows

Paulo, an engineer who works with me,  found this post without a response, and today we have the answer

You have this line on Sametime.ini

STPresenceSubscriptionsMgr_VM_ARGS=-Xmx1024m -Xgcpolicy:gencon -Xcompactgc

Changed to:

STPresenceSubscriptionsMgr_VM_ARGS=-Xmx768m -Xgcpolicy:gencon -Xcompactgc

Everything works

The problem only happens with Windows 2003 R2 with 4GB RAM.  I'm reopening the PMR to know why.