You can also use GetTableCellFromPoint inside the EVENT_LEFT_CLICK callback as follows:
Point Mouse_Coords;
Point Cell;
Mouse_Coords.x = eventData2;
Mouse_Coords.y = eventData1;
GetTableCellFromPoint (panel, tableID, Mouse_Coords, &Cell);
The output "Cell" will now contain information about the most recently clicked cell; the row number as "y" and the column number as "x". eventData2 and eventData1 are passed through the callback by CVI as the mouse position. I too, struggled with trying to get the true active cell. Good luck.