For 11gR2 upgarde with EBS R12.1 please follow the steps as per belwo note
Interoperability Notes EBS 12.0 and 12.1 with Database 11gR2 (Doc ID 1058763.1)
while upgrade 11gR1 to 11gR2 will not face much issues, before proceedign to upgrade backup the cutom objects
For OS pre-req's please have a look in below mentioned notes
MS Visual Studio 2008 and Visual C++ 2008 Express for Oracle E-Business Suite Release 12 on Windows (Doc ID 1070674.1)
Migrating Oracle E-Business Suite Release 12.1 to Microsoft Windows Server 2008 R2 or 2012 R2
Oracle Applications Documentation Resources, Release 12.1 (Doc ID 790942.1)
Thanks for the update. Please suggest , how to install MKS toolkit and need to install before EBS clone.
I want to clone EBS in Windows server 2008 R2.
Make sure you have the latest cloning patches applied...