Problem calling SQL Server stored procedure from classic ASP

Hi, I'm trying to call a SQL Server 2005 stored procedure from a classic ASP page using ADO.  I have verified that the connection string is correct, the user login has permissions to execute the procedure in question, and that the procedure itself functions properly.  I can reproduce the results in the ASP page by passing in hard-coded SQL.  However, when I call .Execute, I get this error:

Microsoft OLE DB Provider for SQL Server error '80040e14'
Syntax error or access violation

The relevant code snippet is below:

Dim Cmd : Set Cmd = Server.CreateObject("ADODB.Command")
Dim root
With Cmd
  .ActiveConnection = Cn
  .CommandType = adCmdStoredProc
  .CommandText = "getNAIC-ID"
  .Parameters.Append .CreateParameter("@naic_code", adVarChar, adParamInput, 15, Session("SalesImaging_CompanyNum"))
  .Parameters.Append .CreateParameter("@naic_id", adInteger, adParamOutput, ,0)
  .Execute ,,adExecuteNoRecords
  root = .Parameters("@naic_id")
End With

Sorry if I'm missing the obvious - thanks!