The reason may be permissions but if you uninstalled and reinstalled sharepoint please see my previous post as it explains the other reason for this error:firstname.lastname@example.org and I will post them on this blog.
Are you a .NET Developer or Contractor interested in working with Sitecore or Dynamics CRM?
Apply for our Mentorship Program. If accepted, we will mentor you on Sitecore and provide you with project to help you build your skills and make some money at the same time. If you are interested send your resume with details on why you want to work with Sitecore or Dynamics CRM to: Chris Williams - email@example.com or Dennis Augustine - firstname.lastname@example.org We look forward to working with you to achieve your goals.