Subreport Problem

[tupacmoche]

I have a report with three sub-reports and want to insert a new one. The version of Cognos Impromptu that I am using is 7.3.1413.0 This is suppose to be a very simple thing to do but I just can't get it to work. I am putting the List frame (sub-report) on a Form frame but keep getting a cursor with a circle with an X through it, which we know means it can't be done. I have even tried inserting a list frame which I can do and converting it into a sub-report but the option is grayed out under the Reports menu option 'Change to Sub-Report... Does anyone why this is happening?