Activator.CreateInstance

According to the second reference, the Activator.CreateIntance is same as the "new" keyword.

To load the assembly from GAC:

System.Reflection.AssemblyName asmName = new System.Reflection.AssemblyName(name);
System.Reflection.Assembly asm = System.Reflection.Assembly.Load(asmName);
object obj = asm.CreateInstance(typeName);

References:
(1)
http://blogs.msdn.com/haibo_luo/archive/2005/11/17/494009.aspx

(2)
Q&A of Activator.CreateInstance
http://bytes.com/groups/net-c/586685-activator-createinstance-question

(3)
http://mironabramson.com/blog/post/2008/08/Fast-version-of-the-ActivatorCreateInstance-method-using-IL.aspx

(4)
http://blog.lozanotek.com/archive/2006/03/22/8311.aspx

How to upload file using WebClient

To use System.Net.WebClient class, first, you have to create an ASPX page in the website as shown in MSDN website. Then, execute the following:

System.Net.WebClient cli = new System.Net.WebClient();

cli.UploadFile(url,
"POST",
file_name);

Reference:
http://msdn.microsoft.com/en-us/library/system.net.webclient.uploadfile(VS.71).aspx
http://www.developerfusion.com/forum/thread/38843/
http://www.csharpfriends.com/Articles/getArticle.aspx?articleID=115

Handling Exception

Performance testing on catching Exception

http://www.yoda.arachsys.com/csharp/exceptions.html

When to throw exception?

http://blogs.msdn.com/kcwalina/archive/2005/03/16/396787.aspx

Singleton

Check out the discussion of singleton here:
http://www.yoda.arachsys.com/csharp/singleton.html
Sample code extracted from the above URL :

public sealed class Singleton
{
  static Singleton instance=null;
  static readonly object lock_obj = new object();

  Singleton()
  {
  }

  public static Singleton Instance
  {
      get
      {
          if (instance==null)
          {
              lock (lock_obj)
              {
                  if (instance==null)
                  {
                      instance = new Singleton();
                  }
              }
          }

          return instance;
      }
  }
}