Please try this:
1. Open the folder of the project in question.
2. Inside it you should find a file called project.xml, see if there is also an autosave.project.xml file in there.
3. If yes, rename the project.xml to something else like project1.xml
4. Rename the autosave.project.xml file to project.xml
5.Try opening the project again.
If you can not find the autosave.project.xml file please send us the project.xml file so that we can investigate.
For extra safety in the future try using the “Save Incremental” feature which saves that project as a new incremental version.