Windows Phone 7.1 SDK Error

I need your help! "GetCopyToOutputDirectoryContentProjectItems"

I went to a Microsoft Code Camp a few days ago and got all pumped up about the Windows Phone 7.1 release (Mango) SDK.  They handed it out to us. I installed it.  I have tried building many default projects but to no avail, I'm getting the following error:

The target "GetCopyToOutputDirectoryContentProjectItems" does not exist in the project.

WHAT DOES THIS MEAN???? I'm going to lose all my hair from this error.

I'm using the release candidate (not the beta 2, at least I don't think it is...) that was given to us at the Mango Code Camp here in AZ a few days ago.  I tried to uninstall, re-boot, re-install, re-boot.  And all combinations of the same.  Nothing is working.  There is something else I found strange:  Part of the install cannot install the XNA Game Studio plugin and some other XNA item.  I don't have the XNA Game Studio installed.  I' not sure if it the Windows Phone 7.1 SDK tris to install XNA GS or not, but I tried to manually install it and I' getting an error with that as well.  I think that it had to do with the live installer.  I uninstalled it too and tried to install again.  Still same error.  It seems like the project is fine (since this happens on ALL my Windows Phone Projects including one I've tried to target the 7.0 Windows Mobile.  Something seems like it's missing but I cannot figure it out. I'd be happy to send any log files if needed.

FYI, The 3 guys at MS that were there at the phone camp had never seen this error and didn't have any idea what to do other than re-install and re-boot.  No help.  PLEASE HELP!!!  Any other ideas?  Thanks!

Note:  I also uninstalled the Silverlight 4 SDK and even installed the Silverlight 5 SDK once it still did not work and both tries still did nothing to help resolve this.