Client Tools :: Update Failed ORA-01722 - Invalid Number

Enviroment is Embarcadero RAD Studio XE. Work with DataSnap WebBroker Application. Its Server methods ancestor is TDSServerModule.

I've got SQLConnection (dbx), SQLDataSet, DataSetProvider on server side and SQLConnection, DSProviderConnection, ClientDataSet plus DataSource, DBGrid, DBNavigator on client side.
SQLConnection on server side uses Oracle driver - dbxora.dll. DB: Oracle 11g.
SQLConnection on client side uses Datasnap driver.
SQLDataSet has DbxCommandType set to Dbx.SQL, CommandText: "Select * from Table1".
All fields except indexed one have their pfInWhere set to false.
updateMode of DataSetProvaider is set to upWhereKeyOnly.

All is well up to point where ApplayUpdates is fired. It does nothing. HandleReconcileError shows ORA-01722: invalid number.

Oracle explains: ORA-01722:invalid number

Cause: The attempted conversion of a character string to a number failed because the character string was not a valid numeric literal. Only numeric fields or character fields containing numeric data may be used in arithmetic functions or expressions. Only numeric fields may be added to or subtracted from dates.

Action: Check the character strings in the function or expression. Check that they contain only numbers, a sign, a decimal point, and the character "E" or "e" and retry the operation. But all updated fields are of character strings type. There is no need for conversion. I suppose the automatically created SQL has some extra checking. But I cannot see those SQLs. I guess must be a way of controlling those SQLs thru params, but don't know which. May be comparison old value - new value of index column is depending on this conversion?