Difficult problem error -sesssion variable workaround

[SmagO]

Hi all,
I am new to .Net and have a frustrating problem.

We have a peice of code that works, but every now and then we get the attached error. It works fine, but then after many transactions this error pops up. Once the error has popped up - we cant use the page for a while (maybe until the session times out.)

Please take alook...thanks
error:

Object reference not set to an instance of an object. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
 
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
 
Source Error: 
 
 
Line 37:         'Response.Write(drData)
Line 38:         'Response.End()
Line 39:    While drData.Read
Line 40:             strAspxPageToCall = drData("AspxPageToCall")
Line 41:             '   Response.Write(strAspxPageToCall)
 
 
Source File: \\Prxdevtest\Projects\LGWSETA\AdminTools\ToAspxDisplay.aspx.vb    Line: 39 
 
Stack Trace: 
 
 
[NullReferenceException: Object reference not set to an instance of an object.]
   AdminTools.ToAspxDisplay.Page_Load(Object sender, EventArgs e) in \\Prxdevtest\Projects\LGWSETA\AdminTools\ToAspxDisplay.aspx.vb:39
   System.Web.UI.Control.OnLoad(EventArgs e) +67
   System.Web.UI.Control.LoadRecursive() +29
   System.Web.UI.Page.ProcessRequestMain() +724

The code is a work around because we cant pass session variables in .net - so we write the session variables to a database and read them back.