Hi,
Issue was resolved.
Reply from SAP support was:"Please change the screen area from 091to 101and test again (see your attachment "CUSTOM SUBSC.DOC" and note 2271653)"
Based on this we created a new screen area 101 and assign our subscreens to it. It worked.
It turned out that may be we jumped from EHP4 to EHP 7 directly and not in steps.
Thanks again to all for their suggestions.