Problem with Index on BDE5.10!

I work with Delphi4.0 and BDE5.1

1     I have a Problem with Locate,
      because this Operation sometime find Data and sometimes not!

2.     The Indexes on Dbase Table are sometime corrupted,
        and then my Application don't find the Data I need (findkey,

3     When I try to copy a lot of Data to A File with many Indexes
        I get A Read error on the Table I write

Can someone help me???????????