If you stumble across the following error message with Visual Studio 2013 Update 2 RC:

1>[…]\Package.appxmanifest(19,64): error APPX3210: App manifest references the image ‘Assets/Icon150.png’ which does not have a candidate in main app package.

have a look a at the manifest file. In my case I had been using forward slashes in some of the asset paths. While this used to work before update 2 it now leads to an error. So to fix this I had to replace this:

<m2:DefaultTile Square310x310Logo="Assets\Icon310.png" 
  Wide310x150Logo="Assets/Icon150.png">

with this:

<m2:DefaultTile Square310x310Logo="Assets\Icon310.png" 
  Wide310x150Logo="Assets\Icon150.png">

and the error went away.