Update Failed

Delphi 4 question

I am displaying Query1 in a DBGrid.
I am using an UpdateSql component with cached updates set to true for
Query1.
I select records in the DBGrid for deletion.
I execute the "DBGrid.SelectedRows.Delete" aswell as "DBgrid.Refresh".
I execute "Query1.ApplyUpdates".

I get an "Update Failed" dialog box.
This is after I get an "EDatabaseError" Exception.

How do I resolve this?