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.