Why can't I read Oracles CLOB columns via SQL-SERVER 2008 linked server?

I want to access data in an Oracle 11g database from SQL-Server 2008

I set up a linked server and when I execute

select * from [Link_server_name]..Oracle_schema.Oracle_table

and Oracle_table contains Number and varchar2 columns, all works as excepted.

But when the Oracle_table contains a CLOB column, I get the following error:

Der OLE DB-Anbieter 'MSDAORA' für den Verbindungsserver 'L_V407SR8T' hat die Meldung 'Unspecified error' zurückgeben.

Der OLE DB-Anbieter 'MSDAORA' für den Verbindungsserver 'L_V407SR8T' hat die Meldung 'Oracle error occurred, but error message could not be retrieved from Oracle.' zurückgeben.

Der OLE DB-Anbieter 'MSDAORA' für den Verbindungsserver 'L_V407SR8T' hat die Meldung 'Data type is not supported.' zurückgeben.

Msg 7306, Level 16, State 2, Line 1

Die '"MCCAPP"."DOGGRUPPEN"'-Tabelle vom OLE DB-Anbieter 'MSDAORA' für den Verbindungsserver 'L_V407SR8T' kann nicht geöffnet werden.

Using OPENQUERY

SELECT * FROM OPENQUERY([L_V407SR8T], 'Select CLOB_COLUMN from Oracle_table'  )

I get

Der OLE DB-Anbieter 'MSDAORA' für den Verbindungsserver 'L_V407SR8T' hat die Meldung 'Oracle error occurred, but error message could not be retrieved from Oracle.' zurückgeben.
Der OLE DB-Anbieter 'MSDAORA' für den Verbindungsserver 'L_V407SR8T' hat die Meldung 'Data type is not supported.' zurückgeben.

Please excuse German error messages.

My question: Is there any way to read CLOB columns via linked Servers?

EDIT:

• SQL Server Import and Export Wizard

seems to depend on OLE DB too and
sucks on the same tables

• I'm asking myself, if the problem

depends on the character sets uses,
but I can't change them

• As practical work around, I use some

PowerShell scripts to get at the
data, but

Download and install an Oracle 11 database client on your SQL Server 2008 machine.

Set up a linked server using an Oracle OLE DB provider (OraOLEDB.Oracle).

Make sure "Allow InProcess" is enabled in Provider options.

The Oracle 11 OLE DB client supports CLOBs.

StackExchange Database Administrators Q#297, answer score: 3