After installing Visual Studio 2010 Service Pack 1, some users were unable to use the x64 or IA64 compilers from the Windows SDK 7.1. Now the Visual C++ team has released an update for VS2010 SP1 available here. For more information about the update, please see KB2519277 on the Microsoft Support site.

You can install the update to fix existing installations, but if you have not yet installed Visual Studio 2010 SP1 the recommended install order is,

1. Visual Studio 2010 RTM
2. Windows SDK 7.1
3. Visual Studio 2010 SP1
4. Visual C++ 2010 SP1 Compiler Update for the Windows SDK 7.1

Please visit the Visual C++ team blog for more information or questions.