SQL 2005 Optional Feature not Implemented error message

This is the beginning of the stored procedure:
LTER PROCEDURE [dbo].[VO_USP_VOVlUnitPayment]
      @ContractCode as varchar(12),
      @UnitId  as bigint,
      @Month as int,
      @VoucherID as bigint,
      @VoucherDate as varchar(23)

AS

BEGIN..

This is how the VB code deals with parameters:
coVoucher.ActiveConnection = cnConnection
50        coVoucher.CommandType = adCmdStoredProc
60        coVoucher.CommandText = LIST_UNIT_PAYMENTS
70        coVoucher.CommandTimeout = objConnection.CommandTimeout
         
80        coVoucher.Parameters.Append coVoucher.CreateParameter("@int_ReturnValue", adInteger, adParamReturnValue)
         
90        coVoucher.Parameters.Append coVoucher.CreateParameter("@ch_ContractCode", adChar, adParamInput, 12)
100       coVoucher.Parameters("@ch_ContractCode").Value = istrContractCode
          Debug.Print istrContractCode
         

110       coVoucher.Parameters.Append coVoucher.CreateParameter("@UnitId", adInteger, adParamInput)
120       coVoucher.Parameters("@UnitId").Value = IIf(IsNumeric(iUnitId), iUnitId, Null)
            Debug.Print iUnitId
           
121       coVoucher.Parameters.Append coVoucher.CreateParameter("@Month", adInteger, adParamInput)
122       coVoucher.Parameters("@Month").Value = IIf(IsNumeric(iMonth), iMonth, Null)
            Debug.Print iMonth
           
123       coVoucher.Parameters.Append coVoucher.CreateParameter("@VoucherID", adInteger, adParamInput)
124       coVoucher.Parameters("@VoucherID").Value = iVoucherId
            Debug.Print iVoucherId
           
125       coVoucher.Parameters.Append coVoucher.CreateParameter("@VoucherDate", adDate, adParamInput)
126       coVoucher.Parameters("@VoucherDate").Value = dtVoucherDate
            Debug.Print dtVoucherDate
           
130       rsVoucher.CursorLocation = adUseClient
140       rsVoucher.Open coVoucher

I used the Debug.Print to get the parameters value and executed the above sp without an error.

But from the vb code on line 130 I am receiving the error message:
"Optional feature not implemented"

Please experts help me understand why and how am  I to fix it?