Если IBEBlock возвращает пустой НД, то при попытке прокрутить его колесом мыши возникает исключение:
IBExpertmtBlock: Cannot perform this operation on a closed dataset

[004FFEAB] Db.DatabaseError (Line 2171, "DB.pas" + 2) + $36
[0050C0B1] Db.TDataSet.CheckActive (Line 8272, "DB.pas" + 1) + $1B
[0050F178] Db.TDataSet.CheckBrowseMode (Line 9936, "DB.pas" + 1) + $4
[0050E5B0] Db.TDataSet.Next (Line 9478, "DB.pas" + 2) + $5
[00984B9A] dxTL.TCustomdxTreeList.GotoNodeByNavigation (Line 5860, "dxTL.pas" + 6) + $F
[0098E4FC] dxTL.TCustomdxTreeList.WndProc (Line 9517, "dxTL.pas" + 47) + $4
[00444170] Forms.StdWndProc (Line 1459, "Forms.pas" + 8) + $0
[0044D97F] Forms.TApplication.ProcessMessage (Line 6630, "Forms.pas" + 13) + $1
[011076D2] IBExpert.IBExpert (Line 935, "D:\Projects_5\IBExpert\IBExpert.dpr" + 147) + $7
Пример блока для тестирования: