Old ASP.NET code works on one computer, not on another? - asp.net

Question

So in my global.asax, I've got the following code:
Inventory.BusinessTier bt = new Inventory.BusinessTier();
string UserLogin = bt.ExtractLogin (Request.ServerVariables ["AUTH_USER"]);
Inventory.User myUser = new Inventory.User (UserLogin);
Session ["User"] = myUser;
It works just fine on one development PC, but using the same version of Visual Studio, it craps out on the third line with this error:
System.TypeInitializationException: 'The type initializer for
'Inventory.DataTier' threw an exception.'
Inner Exception
NullReferenceException: Object reference not set to an instance of an
object.
Other than a line adding impersonation in my web.config (it has to be there now), I haven't changed a single thing. Is there a way to get more info on this? I can't even trace it, because if I put a debug line in the User object constructor, it never hits it. I'm at a bit of a loss. Would appreciate any advice.
EDIT to answer questions below:
InventoryUser is a very simple user object that reads the current from the database and stores some basic user info in properties, such as UserID, Role, RoleID, and IsAdmin.
The DataTier class is a class that interacts with the database. It is used in multiple projects, so I'm quite sure it's not the problem. I tried to paste in the code anyway, but it exceeded the limit for a post.
I'm reasonably sure the problem is related to the user class. It's short, so I can paste it in here:
using System;
using System.Data;
// This is the user business object. It contains information pertaining to the current user of the application. Notably, it
// contains the department ID, which determines what inventory items the user will see when using the application. Only
// specified employees with admin access can see all items for all departments, and that is determined by a specific department ID.
namespace Inventory {
public class User {
private Guid _UserID;
private Guid _RoleID;
private Guid _UserDepartmentID;
private string _UserRole = "";
private string _UserName = "";
private bool _IsAuthorizedUser = false;
private bool _IsAdmin = false;
// Attribute declarations
public Guid UserID {
get {
return _UserID;
}
set {
_UserID = value;
}
}
public string UserRole {
get {
return _UserRole;
}
set {
_UserRole = value;
}
}
public Guid RoleID {
get {
return _RoleID;
}
set {
_RoleID = value;
}
}
public string UserName {
get {
return _UserName;
}
set {
_UserName = value;
}
}
public Guid UserDepartmentID {
get {
return _UserDepartmentID;
}
set {
_UserDepartmentID = value;
}
}
public bool IsAdmin {
get {
return _IsAdmin;
}
set {
_IsAdmin = value;
}
}
public bool IsAuthorizedUser {
get {
return _IsAuthorizedUser;
}
set {
_IsAuthorizedUser = value;
}
}
// -----------------
// - Constructor -
// -----------------
public User (string UserLogin) {
string ShortUserLogin = ExtractLogin (UserLogin);
GetUser (ShortUserLogin);
}
// ------------------
// - ExtractLogin -
// ------------------
public string ExtractLogin (string Login) {
// The domain and "\" symbol must be removed from the string, leaving only the user name.
int pos = Login.IndexOf (#"\");
return Login.Substring (pos + 1, Login.Length - pos - 1);
}
// -------------
// - GetUser -
// -------------
// This method is called to fill the user object based on the user's login. It ultimately gets authorized user data
// from the user table.
public void GetUser (string UserName) {
DataTier dt1 = new DataTier();
DataTable dt = dt1.GetUserInfo (UserName);
int RecordCount = dt.Rows.Count;
switch (RecordCount) {
case 1: // There is one user name match, as there should be. This is the likely situation.
DataRow dr = dt.Rows[0];
UserID = (Guid)dr ["UserID"];
UserRole = (string)dr ["UserRole"];
RoleID = (Guid)dr ["RoleID"];
this.UserName = UserName;
UserDepartmentID = (Guid)dr ["DepartmentID"];
IsAdmin = (bool)dr ["IsAdmin"];
IsAuthorizedUser = true;
break;
case 0: // There are no user name matches (unauthorized use).
IsAdmin = false;
IsAuthorizedUser = false;
break;
default: // There are multiple user name matches (problem!).
IsAdmin = false;
IsAuthorizedUser = false;
break;
}
}
}
}