Hallo,
I have the same problem.
My new Arena 6 seems not to like the compositions I created with Arena 5.
When I try to load any of them, A6 simply ignores it.
The new installation has updated the association to the .avc files, so they all now show the new A6 icon, but even if I double click on the .avc file, Arena 6 starts but showing just a new comp.
Thanks for any advice.
Roberto