Netfabb access violation

Hello!
Just to outline where I'm up to, I've only been using my printer for a couple of months or so and it's wonderful! I love it. I have started scanning and my first scan (just a test cat skull) was great and I was able to do some basic editing and print it in two halves - lovely! I have been scanning models which I have made myself in sections with the idea I would fix them together and then split them up for printing. I have just had my Mac upgraded so it can perform more easily but there are some problems:
1) I can't open anything on Netfabb basic without getting some kind of error message. This includes that 'you do not use enhanced display functions' which I have searched and can find nothing about, also 'could not connect (61)' again - no idea! And when I try to open or import an OBJ or STL then I get a message saying 'access violation'
Meshmixer turns my scans into sphere when I inspect them and they disappear altogether when I repair them.
I have also got myself mudbox and maya but I'm still very much learning how to use them! I really just want to repair my mesh and make it good so I can use Mudbox feeling confident that my files are okay before I chop them up to print.
I'd dearly love some help. I'm beginning to feel a bit lost!
Nicola