CRM 2011 Update System User when New account created - attributes

Question

I am trying to populate a field in the system user entity whenever a user creates an account. I keep getting errors when trying to retrieve the system user entity so that I can populate its attributes. My code is as follows:
public void Execute(IServiceProvider serviceProvider)
{
ITracingService tracingservice = (ITracingService)serviceProvider.GetService(typeof(ITracingService));
IPluginExecutionContext context = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
IOrganizationServiceFactory factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
IOrganizationService service = factory.CreateOrganizationService(context.InitiatingUserId);
if (context.InputParameters.Contains("Target") &&
context.InputParameters["Target"] is Entity)
{
try
{
//Get entity that fired plugin
Entity entMain = (Entity)context.InputParameters["Target"];
//Make a String for the last activity entity
String strLastEntity = "";
//Make the entity for the user entity
Entity entUser = (Entity)service.Retrieve("systemuser", context.InitiatingUserId, new ColumnSet(new String[] { "new_lastactivityentity" }));
//Get the entity type that fired the plugin and set it to the right field for the user entity
if (entMain.LogicalName.Equals("account"))
{
strLastEntity = entMain.LogicalName;
entUser["new_lastactivityentity"] = strLastEntity;
}
}
catch (Exception ex)
{
tracingservice.Trace("FollowupPlugin: {0}", ex.ToString());
throw;
}
}
}
The error is:
Could not load file or assembly 'PluginRegistration, Version=2.1.0.1, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.
Can someone explain how to get the system user so I can update its attributes?

Answer 1

It is because you have an assembly reference that isn't installed on the server, in particular that is PluginRegistration.
You could place that dll in the GAC on the server, however this won't work for CRM Online (or in a Sandbox registration I believe).
Is PluginRegistration a reference to the Microsoft assembly used in the plugin registration tool? Generally speaking you don't need a reference to that in your project, so you could try removing the reference.