Hi Denis.
Checking the box for a position listing result should add it to the selected items list (different of course to selecting the result and having it open the details panel).
By default there is a limit of 50 items permitted in that selection area so if you try to exceed that by adding a 51st entry you would receive that message. If you clear the entries then you may be able to add it in without issue.
I'm not sure what data criteria might preclude a position from being included. After all you may just want to produce a print. So thinking beyond the limit of 50 items, try reviewing the information shown in the details panel for the position (or positions) you are trying to add vs. a selection of positions that can be added. Any common differences?
Regards,
Stephen.
