We have seen this error in some early beta version of the GroupWise 7 client where the Mime.822 file was not available. Later version of the GroupWise client has fixed this issue.
Which version of the GroupWise client you are running (See Help – About GroupWise)? Which version of the solution you are running (See the About option from the Main dialog)? If you are not running the latest point release of the GroupWise client then you may need to upgrade the client.
Hope this helps. We look foward to hearing from you.