>>I have recently upgraded OS from 2003 to 2008 R2 which has ERP 6.0 EhP3 business suite.<<
I am wondering what made you do an in-place upgrade of Windows as it is not supported.
Are you following the SUM guide for starting the SUM tool? Have you tried starting the tool using the STARTUP.BAT from the command prompt as suggested in the guide?
Cheers
RB