What are the correct ADO parameter types for storing a BLOB to sql server

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VB

ASP

ADO

I'm wrestling with the correct parameter definition to use when attempting to store a file to a SQL server db using a stored procedure. The sproc needs to save the record and return the key/id to the caller. Sproc parameters look like this:

procedure sp_insert_attachment @attachment_id char(25) OUTPUT, @digital_image varbinary(max), @comments varchar(max),
           @file_name varchar(max), @file_size numeric(18,2), @parent_table varchar(50), @parent_id char(25), @import_date  datetime,
           @add_user  char(25), @add_datetime datetime

as

SET @attachment_id = CONVERT(CHAR(25), Substring(Replace(Newid(), '-', ''), 1, 25))

INSERT INTO [i_attachment]
           ([attachment_id]
           ,[digital_image]
           ,[comments]
           ,[file_name]
           ,[file_size]
           ,[parent_table]
           ,[parent_id]
           ,[import_date]
           ,[add_user]
           ,[add_datetime]
           ,[status])
     VALUES
           (@attachment_id,
           @digital_image,
		   @comments,
           @file_name,
		   @file_size,
		   @parent_table,
		   @parent_id,
		   @import_date,
           @add_user,
		   @add_datetime,
		   'A')

I've gone through several permutations of parameter types. Currently, this is what I have:

set g_rst = Server.CreateObject("ADODB.Command")
g_rst.CommandText = "sp_insert_attachment"
g_rst.ActiveConnection = Mconn
g_rst.NamedParameters = true
g_rst.CommandType = adCmdStoredProc
g_rst.Parameters.Append(g_rst.CreateParameter("@attachment_id", SqlDbType.Char, adParamOutput))
g_rst.Parameters.Append(g_rst.CreateParameter("@digital_image", SqlDbType.VarBinary, adParamInput, objUpload.Form("FILE1").SaveAsBlob ))
g_rst.Parameters.Append(g_rst.CreateParameter("@comments", SqlDbType.VarChar, adParamInput, -1,  g_strNarrative))
g_rst.Parameters.Append(g_rst.CreateParameter("@file_name", SqlDbType.VarChar, adParamInput, -1,  g_strFileName))
g_rst.Parameters.Append(g_rst.CreateParameter("@file_size", SqlDbType.Decimal, adParamInput, g_dblFileSize))
g_rst.Parameters.Append(g_rst.CreateParameter("@parent_table", SqlDbType.VarChar, adParamInput, 50, "event"))
g_rst.Parameters.Append(g_rst.CreateParameter("@parent_id", SqlDbType.Char, adParamInput, 25, g_strEventID))
g_rst.Parameters.Append(g_rst.CreateParameter("@import_date", SqlDbType.DateTime2, adParamInput, DateTime.Parse(now())))
g_rst.Parameters.Append(g_rst.CreateParameter("@add_user", SqlDbType.Char, adParamInput, 25, session("sec_user_id")))
g_rst.Parameters.Append(g_rst.CreateParameter("@add_datetime", SqlDbType.DateTime2, adParamInput, DateTime.Parse(now())))

g_rst.Execute

'g_strAttachmentID = g_rst.Parameters("@attachment_id").Value

g_rst.Close

This is throwing a -2147217900 error. Any help is greatly appreciated.