I have found similar problems when using pan and zoom with dissolves... I think Studio 12 has a memory management problem, since smaller pieces of the same movie seem to work fine.
I suggest you break your project into 1-2 minute segments (Proj1, Proj2, Proj3, etc), render them as .mpg files, then create a new project that simply brings them all together. No need to change anything IN the project.
Be careful if you break on a transition, since it will chop part of each video! Best to break cleanly... I've had to do this with two other projects and, although cumbersome, it seems to work (my projects had video, still overlays, pan/zoom, dissolves, .mp3 music files, etc..)