I need to create a Lookup Field where the user can select a single item or multiple items. The User Guide says to use the Display Type in the Field's Property Sheet to select "Multi-select" to achieve this. Yet when I use the Lookup Field's Property Sheet, the Display Type is greyed out and disabled. My Lookup links to a table of items which I want to be able to ad to - so I don't want to use a Multiselect field type which only allows for a static list of items.

Can anyone advise me?

Thanks!