[CRM 2011] Strange error SOMETIMES happens when creating users from code

Sometimes I get the following error when attempting to create a user programmatically from our application.

The Web Service plug-in failed in OrganizationId: 6179c202-d76e-e311-bf63-f46d048de5bd; SdkMessageProcessingStepId: 5acabb1b-ea3e-db11-86a7-000a3a5473e8; EntityName: systemuser; Stage: 30; MessageName: Create; AssemblyName: Microsoft.Crm.Extensibility.InternalOperationPlugin, Microsoft.Crm.ObjectModel, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35; ClassName: Microsoft.Crm.Extensibility.InternalOperationPlugin; Exception: Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Web.Services.Protocols.LogicalMethodInfo.Invoke(Object target, Object[] values)
   at Microsoft.Crm.Extensibility.InternalOperationPlugin.Execute(IServiceProvider serviceProvider)
   at Microsoft.Crm.Extensibility.V5PluginProxyStep.ExecuteInternal(PipelineExecutionContext context)
   at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context)
Inner Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
   at System.DirectoryServices.DirectoryEntry.Invoke(String methodName, Object[] args)
   at Microsoft.Crm.SecurityUtils.AddPrincipalToGroupByName(String principalName, Guid groupId, Boolean limitGlobalCatalogSearches)
   at Microsoft.Crm.SecurityUtils.AddPrincipalToGroupByName(String principalName, Guid groupId)
   at Microsoft.Crm.BusinessEntities.SecurityLibrary.AddPrincipalToGroupByName(String NTName, Guid groupId)
   at Microsoft.Crm.Authentication.UserManagementFactory.CheckForActiveDirectoryUser(String uniqueName, UserValidationParameters userValidationParameters, ExecutionContext context, Boolean limitGlobalCatalogSearches)
   at Microsoft.Crm.Authentication.UserManagementFactory.ValidateActiveDirectoryUser(String domainName, UserValidationParameters userValidationParameters, ExecutionContext context, Boolean limitGlobalCatalogSearches)
   at Microsoft.Crm.Authentication.UserManagementFactory.CreateUser(IBusinessEntity systemUser, Boolean setupUser, ExecutionContext context)
   at Microsoft.Crm.ObjectModel.SystemUserServiceInternal`1.CreateInternal(Guid organizationId, IBusinessEntity systemuser, ExecutionContext context)
   at Microsoft.Crm.ObjectModel.SystemUserServiceInternal`1.Create(IBusinessEntity systemuser, ExecutionContext context)
Inner Exception: System.IO.FileNotFoundException: The system cannot find the file specified.


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This is the Event Viewer log - the actual exception that I receive in code is unhelpful ("Unexpected error has occurred"). When this error occurs then the issue persists for a number of minutes before resolving on its own.

What could be the reason? Is there a workaround?