NULLReferenceException From SqlDataReader.GetValue()

I am getting a random exception coming out of ADO.NET's SqlDataReader that I can't seem to track down for the life of me. I have put SQL Server and IIS under heavy load, with neither giving me the exceptions except occasionally (they come when there is no load as well). Web Site is built in VS2005 using .NET 2.0.

Basically, I have a web page that caches a few tables from a SQL database (about 10 tables are loaded into cache from this page) and the error can come from any of the tables while they are being read from the database randomly. I had assumed it was possible that a timeout was occuring while reading the data but from what the brief results google shows, there would be a different exception thrown it a timeout had occured.

 Here is the exception that is showing up:

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Data.SqlClient.SqlDataReader.ReadColumnHeader(Int32 i)
   at System.Data.SqlClient.SqlDataReader.ReadColumn(Int32 i, Boolean setTimeout)
   at System.Data.SqlClient.SqlDataReader.GetValueInternal(Int32 i)
   at System.Data.SqlClient.SqlDataReader.GetValue(Int32 i)
   at Library.Data.DataProxy.ExecuteStoredProcedure(ArrayList& returnValues, TypeFactory factory)

I got the following exception once from the same section of code as well:

System.InvalidOperationException: Invalid attempt to FieldCount when reader is closed.
   at System.Data.SqlClient.SqlDataReader.get_FieldCount()
   at Library.Data.DataProxy.ExecuteStoredProcedure(ArrayList& returnValues, TypeFactory factory)

The code generating these errors is on line 29 below:

1    /// <summary>
2    /// Executes a stored procedure that returns values
3    /// </summary>
4    /// <param name="returnValues">An arraylist of Types</param>
5    /// <param name="factory">The Type specific factory</param>
6    /// <returns>True if successful, false otherwise</returns>
7    public bool ExecuteStoredProcedure(out ArrayList returnValues, TypeFactory factory)
8    {
9        bool bResult = true;
10       SqlDataReader reader = null;
11  
12       returnValues = new ArrayList();
13       MenseType nextType = null;
14  
15       try
16       {
17           // Open database connection
18           OpenConnection();
19  
20           // execute SP
21           reader = m_sqlCommand.ExecuteReader();
22                  
23           while(reader.Read())
24           {
25               nextType = factory.CreateInstance();
26  
27               for(int i = 0; i < reader.FieldCount; i++)
28               {
29                   object val = reader.GetValue(i);
30  
31                   if(DBNull.Value == val)
32                       val = null;
33                          
34                   nextType.SetValue(reader.GetName(i), val);
35               }
36  
37               returnValues.Add(nextType);
38  
39           } // while
40  
41       } // @ try
42       catch(Exception ex)
43       {
44           returnValues = null;
45           m_LastError = ex.ToString();
46           bResult = false;
47  
48           #if(DEBUG)
49           Library.IO.Logging.AddSQLMessage(ex);
50           #endif
51  
52       } // @ catch
53       finally
54       {
55           // close the reader if nessessary
56           if (null != reader)
57               reader.Close();
58  
59           // close db connection
60           CloseConnection();
61  
62       } // @ finally
63  
64       return bResult;
65          
66   } // ExecuteStoredProcedure()


Any input would be greatly appreciated.