For users of Windows XP SP3 you are getting the message “The remote computer requires Network Level Authentication, which your computer does not support.”
You have two options to fix this:
1) Update your remote desktop client to the latest version (v7.0) http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=20609
2) Enable your existing v6.1 RDP client for the Credential Security Support Providerhttp://support.microsoft.com/kb/951608/
You will need to be an administrator of your machine to be able to perform the above.