Diagnosis
On the item overview, you have selected a number of items in order todisplay the detail screen for these items.
You are now looking at the detail screen of one of the selected itemsand want to get the same data from the next selected item usingfunction item +.
As the data you are looking at is from the last selected itemwithin the item overview, this message appears.

Procedure
Choose function Item - to move in the other direction or go backto the item overview using function key F3 and reselect as required.