Hi Andy
After it did it a couple off times of trying to save some complex shapes I tried using a simple cube, again it crashed...so I went back and deleted the whole programme including the original download. After uploading a new version (2nd time) It is working ok again and I'm able to save
I am now wondering if operator error is the culprit or my windows? Anyway good news is I'm up and running again and loving the useability and simplicity of AC3D. I just need to keep saving my work at regular interviews in case the bug appears again!