Len() is for counting the number of elements within a single string, CountRows() is for counting how many items there are (i.e. how many items are selected). You are trying to determine if there is a valid item(s) selected.
In your example, you are referencing .SelectedItems which is a multiple-item property
You can either do the following for a singular selected item (assuming this is a single-select-only combobox)
Len(datacardvalue7.Selected.Value) > 0
(it may be another property than .Value)
Or you can reference the number of selected items, but from your description it sounds like you want to check whether the selected item itself is valid rather than the number of selected items:
CountRows(datacardvalue7.selecteditems) > 0
Cheers,
Sancho
