"Plug-in assembly fullnames must be unique" on updating plugin registration - dynamics-crm-2011

Question

Dynamics CRM 2011 on premise.
I registered a custom workflow assembly using the Plugin Registration Tool.
The plugin code was:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Activities;
using Microsoft.Xrm.Sdk;
using Microsoft.Xrm.Sdk.Workflow;
namespace CreateDirectDebit
{
public class CreateDirectDebit : CodeActivity
{
protected override void Execute(CodeActivityContext context)
{
}
}
}
This was successful.
Then I change the code to this:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Activities;
using Microsoft.Xrm.Sdk;
using Microsoft.Xrm.Sdk.Workflow;
namespace CreateDirectDebit
{
public class CreateDirectDebit : CodeActivity
{
protected override void Execute(CodeActivityContext context)
{
// Create the tracing service
ITracingService tracingService = context.GetExtension<ITracingService>();
if (tracingService == null)
throw new InvalidPluginExecutionException("Failed to retrieve the tracing service.");
tracingService.Trace("CreateDirectDebit.Execute, 1");
throw new InvalidPluginExecutionException("Testing dialog custom workflow.");
}
}
}
When I update the assembly using the Plugin Registration Tool I get this error on pressing Update Selected Plugins:
Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: Plug-in assembly fullnames must be unique (ignoring the version build and revision number).
Detail: <OrganizationServiceFault xmlns="http://schemas.microsoft.com/xrm/2011/Contracts" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<ErrorCode>-2147204741</ErrorCode>
<ErrorDetails xmlns:a="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
<Message>Plug-in assembly fullnames must be unique (ignoring the version build and revision number).</Message>
<Timestamp>2013-10-14T10:04:55.4528719Z</Timestamp>
<InnerFault>
<ErrorCode>-2147204741</ErrorCode>
<ErrorDetails xmlns:a="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
<Message>Plug-in assembly fullnames must be unique (ignoring the version build and revision number).</Message>
<Timestamp>2013-10-14T10:04:55.4528719Z</Timestamp>
<InnerFault i:nil="true" />
<TraceText i:nil="true" />
</InnerFault>
<TraceText i:nil="true" />
</OrganizationServiceFault>
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)
The same error occurs if I revert the code to the first version and try to update the assembly.
What have I done wrong?

Answer 1

This usually arises for one of two reasons:
You've clicked Register rather than Update in the Plugin Registration Tool
You've clicked Update but you had selected the wrong plugin/workflow assembly to update.

Answer 2

In Dynamics CRM 2011 plugin and workflow assemblies can be updated as long as name, public key, major version and minor version of existing and new assemblies are the same. If the minor version of your assembly has been incremented (your VS build may have done this automatically), then both are considered to be different.
They can however be registered side-by-side. Just register the new version and remove the old one.

Answer 3

In my case, I received this error when trying to update a plugin.
The plugin I had selected to update in the Registered Plugins & Custom Workflow Activities area wasn't correct. The names were very similar so I didn't notice at first.
By selecting the correct plugin to update from the list, I was able to continue with the update.

Answer 4

Your assembly must be strongly signed with the full strongname matching. The two most likely culprits are the version number and that you've used a different key to sign the assembly.
I wrote up a blog post with more info:
PLUGIN ASSEMBY FULLNAMES MUST BE UNIQUE
http://helpfulbit.com/plugin-assemby-fullnames-must-be-unique/