VB collection取值问题. 在线等!

我写了一个函数从ORACLE函数内取出一个数据集.将数据集的第二个字段做为Collection的KEY 第三个字段做为Collection的VALUE  将Collection返回出去. 在外面NEW一个Collection来接收这个Collection  在取值的时候发现COUNT有98 当我a.Item("xh")取值时则出现异常. RUNTIME ERROR为3420 错误信息是对象不再有效. 这是怎么回事??  代码在下面. 各位大大帮我看下.谢谢!
=================================这段是Function体==============================================
Public Function CallService(ByVal serialNo as string,byval invalue as string ,byval servicename as string) as Collection

Dim Con As New ADODB.Connection
Dim Rst1 As New ADODB.Recordset
Dim xItems As New Collection
Dim Cmd As New ADODB.Command
Dim Prm1 As New ADODB.Parameter
Dim Prm2 As New ADODB.Parameter
Dim Prm3 As New ADODB.Parameter
Dim Prm4 As New ADODB.Parameter

Con.Provider = "OraOLEDB.Oracle"
Con.ConnectionString = "Data Source=edb.stc.gov.cn;" & _
"User ID=itosc;Password=itosc;PLSQLRSet=1"
Con.Open
Set Cmd.ActiveConnection = Con
Cmd.CommandType = adCmdText

Dim prm As New ADODB.Parameter
Set prm = Cmd.CreateParameter("l_request", adSmallInt, adParamReturnValue)
Cmd.Parameters.Append prm
Set Prm1 = Cmd.CreateParameter("SerialNo", adBSTR, adParamInput, , serialNo)
Cmd.Parameters.Append Prm1
S