Thanks. In the report there was a component layout reference that was referring to a broken path. In my expectation, this should not prevent the report from opening up. It should open up the report in report studio and the references should be shown as 'Component Reference Not found'.
But anyway Cognos does not even open up the report if the component reference refers to a path that is broken/moved etc.
To solve this, I recreated the broken path and then opened up the report and then corrected the component references.