Thanks Lockwelle.
More Info:
The main report is very simple. Is is a "roster" report, so we have employees, the date, their start time, and their location. The main report has parameters to select the date and the locations for the rosters we want to see. The locations are strings, eg "Cafe", "Kitchen", "Bar" etc. The Main Report is Grouped by Employee. The Sub Report is in the Employee Group and it has to pick up the employee, the date, and the locations. But where I have selected for example "Cafe" and "Kitchen" in the main report, the sub report is only showing one location. So an employee that is rostered only to "Cafe" is fine, or just to "Kitchen" is fine, but where an employee is rostered to both "Cafe" and "Kitchen" it is onlying showing one of the locations.
The reason why I'm using the Sub Reports is to create a column for each date (Monday, Tuesday etc) so it kinda looks like a table.
What do ya think?