Hello Saurabh
With your upgrade to 6.1 your default Global parameter probably got changed. You can check under transaction SICF for Web Dynpro Application WD_GLOBAL_SETTING
Run SICF and enter WD_GLOBAL_SETTING in the service name. Then execute, then right click on WD_GLOBAL_SETTING and test the service. Scroll down to the Design area and take a look at Stylesheet as well as the UI Guideline values (compare this to your PPM 5 system if still available).
Does this help?
Regards
C