Run-time error when using OraOLEDB.Oracle Provider

Hello everyone,
I have faced the following problem. I had a perfectly working code to call oracle stored procedures using MSDAORA. However, connection to Oracle DB doesn't work from Win 64-bit. AFAIK Microsoft doesn't support MSDAORA driver for 64bit Windows, so that I will need to use another driver. I have set up the connection using Oracle Provider for OLEDB. However, I have difficulties calling stored procedures, and unfortunately cannot find any code..

Here's the initial code, that worked perfectly:

Code:

---

Sub connection()
    Dim cn As ADODB.Connection
    Dim cmd_prod As New ADODB.Command
    Set cn = New ADODB.Connection
    With cn
        .ConnectionString = "Provider=MSDAORA.1;Data Source=datasrc;User Id=user_id;Password=pwd" 'I omit declaration and initialization of these variables
        .CursorLocation = adUseClient
      .Open
    End With
    With cmd_prod
        Set .ActiveConnection = cn
        .CommandText = "s#mdb$stg_da_extr_util.get_all_secevt_ot_aft_mpa_ids"
        .CommandType = adCmdStoredProc
        Set ParamReturn = .CreateParameter("rslt_ot_aft", adLongVarChar, adParamReturnValue, 10000000)
        .Parameters.Append ParamReturn
        Set i_caller = .CreateParameter("Caller Identification", adVarChar, adParamInput, 50, "STG_DATA_REQUEST")
      .Parameters.Append i_caller
      .Execute , , adExecuteNoRecords
      ot_aft = .Parameters("rslt_ot_aft")
      varSplit = Split(ot_aft, ";")
      'first row
      row = 2
      'first column
      col_cnt = 1
        For i = 0 To UBound(varSplit)
            idx = varSplit(i)
            'here the data is splitted and excel tables are populated           
            ...
        Next i
  End With

---

Now I have changed the connection string to the following:

Code:

---

    With cn
        .ConnectionString = "Provider=ORAOLEDB.Oracle;Data Source=" & ih.Cells(1, 2) & ";User Id=" & ih.Cells(2, 2) & ";Password=" & ih.Cells(3, 2) & " "
        .CursorLocation = adUseClient
        .Open 'the code breaks here stating: Run-Time error '3706' Provider cannot be found. It may not be properly installed.
    End With

---

Can anyone please give me a hint what am I doing wrong?

The Oracle client 11.0.2 is installed.