To overcome this problem we have to install Windows Management framework 3.0 on windows 2008/2008r2 computers.(* if we are managing these servers from windows 2012 R2, we have to install management framework 4.0
)
After that we need to enable remote management from the powershell
(Set-ExecutionPolicy remotesigned
Configure-SMRemoting.ps1 -force -enable)
Now we can manage 2008/2008r2 servers from windows 2012 server manager