Cannot insert duplicate key - Warning in CRM 2011 server

Hi,

This is the error description from one of our server.

Exception information:

    Exception type: CrmException

    Exception message:Cannot insert duplicate key.

   at Microsoft.Crm.Application.Platform.ServiceCommands.PlatformCommand.XrmExecuteInternal()

   at Microsoft.Crm.Application.Platform.ServiceCommands.CreateCommand.Execute()

   at Microsoft.Crm.Application.Platform.AppFormFilter.SetLastViewedForm(Guid formId)

   at Microsoft.Crm.Application.Forms.CustomizableForm.GetFormDescriptor(Int32 typeCode, FormType formType)

   at Microsoft.Crm.Application.Forms.CustomizableForm.Execute(Entity entity, FormType formType)

   at Microsoft.Crm.Application.Components.PageHandlers.AccountRecordPageHandler.ConfigureFormHandler()

   at Microsoft.Crm.Application.Components.Utility.GenericEventProcessor.RaiseEvent(String eventName)

   at Microsoft.Crm.Application.Controls.PageManager.OnPreRender(EventArgs e)

   at System.Web.UI.Control.PreRenderRecursiveInternal()

   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Could any body help me with this.

Sreeni Pavalla