PROBLEM:
When using Remote Desktop Connection in Windows XP to connect to other versions of Windows you will get the following error:
"The remote computer requires Network Level Authentication, which your computer does not support."
RESOLUTION:
1) Ensure that Windows XP has Service Pack 3 installed.
2) Open RegEdit
3) Navigate to: HKLM\SYSTEM\CurrentControlSet\Control\Lsa
4) Modify SECURITY PACKAGES. In the Value data box, type "tspkg" and be sure to not delete any other data.
5) Navigate to: HKLM\SYSTEM\CurrentControlSet\Control\Security Providers
6) Modify SECURITY PACKAGES. In the Value data box, type "crddssp.dll" and be sure to not delete any other data.
7) Exit RegEdit, and restart the computer.
If you're still getting the same error review the edited registry keys to ensure that the correct values were added.