You just want the error message to be displayed on the default SharePoint error page. Is this an easy

In Microsoft.SharePoint.Utilities.SPUtility there are 2 functions:

  • SPUtility.TransferToErrorPage - this transfers the user to the administrative layouts page for error messages
  • SPUtility.TransferToSuccessPage - this transfers the user to the page one would see after something such as a long running transaction

There are a few overloads for each and they come in handy when developing custom admin pages or custom lists.