Do the scene files use 3rd party light sets or custom light sets that you didn't add to this install of P7.

Back in the early days of P7, I had issues with scene files from P6 opening in P7.  EF tech support told me that I needed to install the custom light sets to P7.  I did and it solved the problems.  Their long explanation didn't make a whole lot of sense to me but it worked so I really didn't care.