Can not load an assembly into an appdomain

[linhnc]

Hi all,
Because I have to load and unload an assembly, so I try to create a new appdomain and load the assembly into it. But it throws an exception with the message "Insufficient state to deserialize the object. More information is needed.". I don't know how to fix this problem. Pls help me. Thanks.
This is my code in C#
public static object CreateInstance(string path)
{
AppDomain extDom = AppDomain.CreateDomain("HELLO");
AssemblyName extName = new AssemblyName();
//this is sample path for DLL file
extName.CodeBase = @"file://C:\\sample.dll";
Assembly extDll=extDom.Load(extName); //exception is throw in this line
Type extType=extDll.GetExportedTypes()[0];
object extObj = extDom.CreateInstanceAndUnwrap(extDll.FullName, extType.FullName);
return extObj;
}

[linhnc]

I have tried many ways, but it can not be resolved. Pls help me. Thanks

[kenobewan]

This error is often caused because it can't load a particular assembly. Make sure the assembly is findable, for example by placing it into the GAC or the
program directory of the .exe which is doing the deserialization. Can you give all the Exception information (call stack, message, etc)?