Error migrating Tridion 2009 event system to Tridion 2011 SP1

After adding my existing Tridion 2009 DLL (compiled on the 2011 server) to the bin directory and registering the DLL in the Content Manager configuration file, the GUI now returns the error below. I checked event logs, Tridion logs, etc., to get more details on the "missing dependency", any ideas?

Could not load file or assembly 'Tridion.Extensions.Events, Version=1.0.20.521,
Culture=neutral, PublicKeyToken=ecb60dbe3cbb7440' or one of its dependencies. 
The system cannot find the file specified.

Unable to get LangID of User (tcm:0-2851-65552). Initialization of the extension
'C:\Program Files (x86)\Tridion\bin\Tridion.Extensions.Events.MDO.dll' failed.

System.Reflection.RuntimeAssembly.GetExportedTypes(RuntimeAssembly,ObjectHandleOnStack) 
    System.Reflection.RuntimeAssembly.GetExportedTypes() 
    Tridion.ContentManager.Extensibility.TcmExtension.LoadExtensions() 
    Tridion.ContentManager.Extensibility.TcmExtension.LoadExtensions() 
    Tridion.ContentManager.Extensibility.TcmExtension.InitializeExtensions() 
    Tridion.ContentManager.Extensibility.EventSystem.DeliverEvent(IEnumerable`1,TcmEventArgs,EventDeliveryPhase) 
    Tridion.ContentManager.Extensibility.EventSystem.DeliverEvent(IdentifiableObject,TcmEventArgs,EventDeliveryPhase) Tridion.ContentManager.IdentifiableObject.Load(LoadFlags,Boolean) 
    Tridion.ContentManager.IdentifiableObject.Load(LoadFlags) 
    Tridion.ContentManager.BLFacade.IdentifiableObjectFacade.Read(UserContext,String,XMLReadFilter) XMLState.GetPropertyElem XMLState.GetProperty User.LangID