Can't save, open or undo something in Blender

I have big project in blender. When I save the file, after this I can’t open it, I have message “DNA block is missing”. Also Undo doesn’t work… So I have no way to finish my project. Blender 2.79b. File size is 4,8 GB may be this is the reason. May be anybody knows what can I do?

4GB might be a limit, but I’m not sure about that. Do you have backups of the scene before it went over 4GB?

I would try opening it in a recent 2.80 (maybe also 2.79 experimental) which might support reading larger files, however if 2.79b didn’t successfully save everything then it might not be valid to load regardless.

When you go to save a .blend file (File->Save As…) there’s an option in the lower left part of the file save window that gives you the option to compress the file which might help if it gets it back under 4GB):