Update Time Error

Hi,

I am new to VB, working in VB 5. I am using RDO 2.0 . My backend is Oracle
8.0. When I insert the record. It works Well but while updating it gives
the error "Client Cursor :12 No Key column are specfied for the update table"
Please help me whats wrong with this.
The code is for update
With rs
.Edit
.rdoColumns.Item(0).Value = Field1.Text
.rdoColumns.Item(1).Value = Field1.Text
.rdoColumns.Item(2).Value = Field1.Text
.update
Thanx in advance
Rakesh