Ghost errors! Please help.

We have a CF application that displays a DataGrid. The
DataGrid contains ItemQty,Department and Item no.
columns. The user either scans or manually input a
Department number on a separate field which causes the
DataGrid to filter the display based on the specified
Department. The user then inputs an Item Qty and updates
the Grid. The problem is after specifying a few
department numbers (or DataGrid filtering), the
application generates an error, but then suddenly
disappears from the screen, so I have no way of knowing
what it is. I tried to use an exception handler, but it
doesn't go there when this type of error occurs. It is
very frustrating. Does anybody experienced this kind of
problem? Please help.