Use older dlls in Metro-Style applications?
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I started work on porting an application I've written for deployment in the Windows 8 app store.  This requires that the application be written against the subset of the .NET framework.  My application follows an architecture where the core functionality is in it's own dll, and things like file system access are done through IoC.  Basically, this means that the only dependency for the core dll is System.  Because of this, I thought that porting would be a breeze - setup my IoC values and wire up a GUI then I'll be good to go. Only, I can't even reference my core dll from the metro style app.

Have I missed something?  Do actually have to rewrite my core dll just for inclusion in the windows 8 app store? We're told that if you use a good architecture, then porting will be a breeze, and that's what I've done.  Has that just been a big lie?