Marco, i have the same problem too.
I dont know in which unit the problem is (it has to do with a TDatalink.Update method). The list index error occurs trying to insert a new record in a Grid in GridMode = True, and only happens with OracleDatasets.
Do you have investigated into this problem ?
I've looked at the DevExpress newsgroup and this should be a Quantum Grid bug. The bug can be reproduced with other datasets (i.e. IBO) too and not just with OracleDataset.
I'm using the 4.5.2 version. The DexEx support has confirmed that this is a know bug and has sent a patched unit.
Are you using the new grid (ver 5.0 ) ?