CRM Dynamics 2011 Plug-in assembly does not contain the required types or assembly content cannot be updated.

Plug-in assembly does not contain the required types or assembly content cannot be updated. 

On registering a plugin using plugin registration tool, you might get this error. Here is more details on the error: Plug-in assembly does not contain the required types or assembly content cannot be updated. 

Detail: -2147204725 CallStack at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context) at Microsoft.Crm.Extensibility.Pipeline.Execute(PipelineExecutionContext context) at Microsoft.Crm.Extensibility.MessageProcessor.Execute(PipelineExecutionContext context) at Microsoft.Crm.Extensibility.InternalMessageDispatcher.Execute(PipelineExecutionContext context) at Microsoft.Crm.Extensibility.ExternalMessageDispatcher.ExecuteInternal(IInProcessOrganizationServiceFactory serviceFactory, IPlatformMessageDispatcherFactory dispatcherFactory, String messageName, String requestName, Int32 primaryObjectTypeCode, Int32 secondaryObjectTypeCode, ParameterCollection fields, CorrelationToken correlationToken, CallerOriginToken originToken, UserAuth userAuth, Guid callerId, Guid transactionContextId, Int32 invocationSource, Nullable`1 requestId, Version endpointVersion) at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.ExecuteRequest(OrganizationRequest request, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType, UserAuth userAuth, Guid targetUserId, Boolean traceRequest, OrganizationContext context, Boolean returnResponse) at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.ExecuteRequest(OrganizationRequest request, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType) at Microsoft.Crm.Extensibility.OrganizationSdkServiceInternal.Update(Entity entity, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType) Plug-in assembly does not contain the required types or assembly content cannot be updated. 2014-07-16T22:10:31.8203518Z -2147204725 CallStack at Microsoft.Crm.CrmPluginAssemblyMetadata.GetPluginTypeMetadata(String typeName) at Microsoft.Crm.ObjectModel.PluginTypeValidator.ValidateInternal() at Microsoft.Crm.ObjectModel.PluginValidatorBase.Validate() at Microsoft.Crm.ObjectModel.AssemblyDataCanBeUpdatedValidator.ValidateInternal() at Microsoft.Crm.ObjectModel.PluginAssemblyServiceInternal`1.VerifyRegistrationAbility(IBusinessEntity pluginAssembly, Boolean createCall, ExecutionContext context) at Microsoft.Crm.ObjectModel.SdkEntityServiceBase.UpdateInternal(IBusinessEntity entity, ExecutionContext context, Boolean verifyAction) at Microsoft.Crm.ObjectModel.PluginAssemblyServiceInternal`1.Update(IBusinessEntity entity, ExecutionContext context) Plug-in assembly does not contain the required types or assembly content cannot be updated. 2014-07-16T22:10:31.8203518Z Server stack trace: at System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation) at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at Microsoft.Xrm.Sdk.IOrganizationService.Update(Entity entity) at Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy.UpdateCore(Entity entity) at Microsoft.Crm.Tools.PluginRegistration.RegistrationHelper.UpdateAssembly(CrmOrganization org, String pathToAssembly, CrmPluginAssembly assembly, PluginType[] type) at Microsoft.Crm.Tools.PluginRegistration.PluginRegistrationForm.btnRegister_Click(Object sender, EventArgs e) 

Reason? 

There could be many reasons for this error message which I am sure there are many articles on the Net talking about it. This was the scenario we faced:

The Plugin which has been registered previously, had a step which has been removed from the assembly! Suppose you have register the plugin assembly with three steps A, B and C. you have then forgot to remove Step B from CRM but you have deleted the corresponding plugin class (The scenario we faced was really we wanted to register the same plugin on a backup org which has an extra step)) 
Hence when you register compiled the new plugin, CRM expects to get "Step B" during plugin update! but considering the class for Step B has been removed and the new assembly does not have it, it throws the error.

How to Solve? 

You need to find out which step needs to be unregistered from the assembly steps before you can update the plugin assembly. If in TFS try to review the history to see what class has been removed and delete the corresponding plugin steps.