Thanks for your suggestion but seems I can't create the UDL32 connection successfully.
I tried to create a UDL (32bit) file, like 'testconn.udl32'. But when I opened the file, I can't find "Oracle Provider for OLE DB" which I can see that in UDL (64bit) file.
Did you follow Test a 32-bit OLEDB Connection With a UDL File on 64-bit Windows [ID 405743.1]?
You should also check 32-bit version of the provider is correctly installed.
You have a master note for troubleshooting OLEDB:
Master Note For The Oracle Provider for OLE DB (OLE DB) (Doc ID 1132946.1)
Make sure to update the TNSNAMES.ORA file with the proper database connect descriptor in the 32Bit Oracle Client\Network\Admin directory.
Sorry I have no access to Oracle Support now.
this error occurs when FDM is unable to connect to the Oracle Database:
Check the following:
a) the 32 bit oracle Client has been installed on the FDM application server
b) the 32 bit Oracle Client TNSNAMES.ORA file has a valid connect descriptor for the database you are entering into the Database Tab. You can test this with a 32 bit UDL file as noted in KM
Test a 32-bit OLEDB Connection With a UDL File on 64-bit Windows (Doc ID 405743.1)
If you are not seeing the Oracle Provider for OLEDB in the 32 bit UDL, then the 32 bit provider has not been installed. You need to make sure that the 32bit RUntime Client, Oracle Provider for OLEDB, Oracle Database Utilities, Oracle Objects for OLE, Oracle Data Provider for .NET and Oracle Providers for ASP.NET are all installed with the 32 bit client installer.
If you are positive that they are installed, you may need to register the oracle provider for OLEDB .dll in the Client\Bin directory with regsrv32