Stored Procedure only partially works??? ASP-> SQL Server

I have a rather difficult question...at least everyone around here makes it sound like it is...that and they have no solutions for me.

I have a SQL Server 2000 database setup, and am trying to call a stored procedure (sp_updateInvcID) from an ASP page.  I am going to cross post this in the ASP forum as well, as I'm not certain where the problem lies (ie. database problem or asp problem).

Table assets
---------------
asst_id identity
asss_id decimal(17)
invc_id decimal(17)
mnfc_id decimal(17)
modl_id decimal(17)
ascr_id decimal(17)
serial_number varchar(30)
asset_number varchar(30)

There are more columns, but these are the ones I am working with.  

sp_updateInvcID
--------------------
CREATE PROCEDURE sp_updateInvcID
      @asstID int,
      @invcID int,      
      @ascrID int,
      @assetNum varchar(30),
      @serial varchar(30)
 AS
      update assets set asss_id=4, invc_id=@invcID, serial_number=@serial,
      asset_number=@assetNum, received_dt=getDate(), paying_ascr_id=@ascrID
      where asst_id=@asstID
GO

ASP JScript to call stored Procedure
------------------------------------------
function updateAssetInvcID(asstID, invcID, ascrID, assetNum, serial) {
      cmd = getStoredProc("sp_updateInvcID");
      cmd.Parameters.Append(cmd.CreateParameter("@asstID", 3, 1, 7, asstID));
      cmd.Parameters.Append(cmd.CreateParameter("@invcID", 3, 1, 7, invcID));      
      cmd.Parameters.Append(cmd.CreateParameter("@ascrID", 3, 1, 7, ascrID));            
      cmd.Parameters.Append(cmd.CreateParameter("@assetNum", 200, 1, 30, assetNum));
      cmd.Parameters.Append(cmd.CreateParameter("@serial", 200, 1, 30, serial));            
      cmd.Execute();      
}

function getStoredProc(name) {
      conn = getConn();
      cmd = Server.CreateObject("ADODB.Command");
      cmd.ActiveConnection = conn;
      cmd.CommandText = name;
      cmd.CommandType = 4;
      cmd.Prepared = true;
      return cmd;
}

function getConn() {
      conn = Server.CreateObject("ADODB.Connection");
      conn.Open = Application("conn");
      return conn;
}

ASP JScript which makes function call
--------------------------------------------
try {
   updateAssetInvcID(asstID, invcID, ascrID, assetNum, serial);
} catch (e) {
  Session("Error") = e.message;
  Response.Redirect("/webapp/error/error.asp");
}            

I have tested all the variables in the try / catch block, and they are all of the appropriate types (ie. strings for assetNum and serial, and integers for the rest).

Here is where things get 'interesting' :(  The way the app works, you may end up updating the invcID of a number of records.  I use a for loop to go through each of the records, calling the same function for each of the records.  For small numbers of records (1-5) the function works MOSTLY fine...but I'll get to that in a second.

For large numbers of function calls, the application fails saying "Arguments are of the wrong type, are out of acceptable range, or are in conflict with one another."

Further, for the 1-5 rows in the table that WERE effected, the asss_id is NOT updated!  I've been struggling with this one for a while now, and asked a lot of people a lot of questions...any further information / suggestions anyone can give are GREATLY appreciated at this point.  

Further info
--------------
IIS 5.0 with appropriate updates / patches
MDAC 2.whatever it's up to
Connection to database is using:
"Provider=sqloledb; Data Source=;User ID=READ;Password=READ" (** Permissions on the database have been set for the read user to execute this stored procedure**)

If anyone needs further information, let me know, and I'll try as best I can to provide it.