Analytics Software

I am not very familiar with Oracle Discoverer but have had to be involved in it recently. What i am trying to do is create a new business area. I logged on to the Oracle Discoverer administrator and followed these steps

- Create a new business area from online dictionary
- Selected the schema user
- Selected the tables/views i wanted to include in the business area
- Click finish

Now i have included the tables in the business area. When the user logs on to Oracle Discoverer he can see the 3 tables/views i selected. If they try to create a new workbook they can only include one of the tables in the workbook but not all 3 at the same time. If i include one table, the other two tables become 'disabled' and cannot be included in the workbook.

Any ideas why this is happening?