ADOExpress/Delphi 5/MS Access plus opdatering

I get an 'insufficient base table information for updating or refreshing'
error when I try to update a record in an Access database using Delphi 5 and
ADOExpress. I have no problems inserting or deleting records.

I do this operations :

// begin update
ADOTable1.Edit;
ADOTable1.FieldByName( 'Date' ).AsDateTime := Now;
ADOTable1.Post;
// end update

What is wrong ?