I am currently trying to create a situation where you first choose a value
from one drop down list, that selection will then control the values that you
can choose from in the secondary dropdown list.

For example you choose that you work with Accounts Payable in the first drop
down list and then you should only be able to select the tasks that Accounts
Payable are performing and not be able to view the tasks that e.g. Accounts
Receivable are performing.

At first my idea was to create a filter from a rule that says that if you
choose Accounts payable only these tasks will be displayed but I get an error
message informing me that no filter can be applied to that list...

Would appreciate any suggestions as I am pretty sure this can be done... I
just don't know how.