Try the following in options:
1.Disabling Auto Recover and Autosave.
2. Unchecking the "open email attachments in reading view".
3.Disabling Protected View.
4.Adding the network folder location to Trusted Locations.
Also you can refer the this link: Excel Repair Toolbox
Hello benyT0,
Try to create a copy of the file and change the extension of the copy to xls (Excel). If iy useless there are many tools which recover Project files.
Try this one Recovery Toolbox for Project
Good luck!