We are going to need to get that file. Ideally, you would open it with 4.1 and use File > Share - Complete to create a .sky.zip file and post that to:
You are the first to encounter this. It must be a pretty large file. It seems we most have introduced a bug in large file handling in 4.2, which we did a lot of work on for 4.1.
If you need 4.1 on a new computer, you can always get any major version from the disconnected installers page.
Click "I Agree" and then click "Archive". These installers are not self-updating. So, eventually you will want to install 4.2 manually when it is fixed for your case.
Thanks for reporting your issue.