Error trying to call Oracle function in VB.NET

hey all,
here is my question. i created this Oracle function i'd like to call in my VB.NET application, but i get the following error:

"Specified cast is not valid."

First, here is the code for creating the Oracle function:

CREATE FUNCTION "ORDERITEMS" (ShippableItemID NUMBER) RETURN NUMBER is
inventory_count NUMBER;
enrollment_count NUMBER;

BEGIN
SELECT InventoryCount INTO inventory_count
FROM SHIPPABLEITEM
WHERE SHIPPABLEITEMID = ShippableItemID
AND Rownum = 1;

SELECT DISTINCT COUNT (COURSERECORD.StudentID) INTO enrollment_count
FROM COURSEINSTANCEMATERIALS, COURSERECORD
WHERE COURSEINSTANCEMATERIALS.ShippableItemID = ShippableItemID
AND COURSERECORD.CourseInstanceID = COURSEINSTANCEMATERIALS.CourseInstanceID;

IF (inventory_count < 0.5*enrollment_count) THEN
RETURN 1;
ELSE
RETURN 0;
END IF;
END;

I tested it in SQL *Plus and it worked fine. Now then, here is the part of my VB.NET code performing the call to the above function:

DBCommand = New ADODB.Command
DBRecords = New ADODB.Recordset
DBCommand.ActiveConnection = DBLink

Dim InputParameter As New ADODB.Parameter
Dim ReturnValue As New ADODB.Parameter

ItemIDValue = DBRecords.Fields(0).Value

DBCommand.CommandText = "OrderItems"
DBCommand.CommandType = ADODB.CommandTypeEnum.adCmdStoredProc

InputParameter.Name = "ShippableItemID"
InputParameter.Direction = ADODB.ParameterDirectionEnum.adParamInput
InputParameter.Type = ADODB.DataTypeEnum.adInteger
InputParameter.Value = ItemIDValue

ReturnValue.Name = "myReturnValue"
ReturnValue.Direction = ADODB.ParameterDirectionEnum.adParamReturnValue
ReturnValue.Type = ADODB.DataTypeEnum.adInteger

'Add parameters to ADODB command.
DBCommand.Parameters.Append(InputParameter) --> ERROR ON THIS LINE
DBCommand.Parameters.Append(ReturnValue)

Try
'Executes the command.
DBFunctionResult = DBCommand.Execute()
Catch ex As Exception
MsgBox("Failed to call Oracle function ORDERITEMS.")
End Try

If Not DBFunctionResult.EOF Then
Do Until DBFunctionResult.EOF
ReturnFlag = DBFunctionResult.Fields(0).Value
MsgBox("Function return value: " & ReturnFlag)
Loop
End If

I get the error in the line marked (DBCommand.Parameters.Append(InputParameter)). I tried setting the type of parameter InputParameter as adNumeric, but got the same error. Any ideas?

Thanks.

uhhh, is this .Net? If so you should be using ADO.Net not ADO 2.x