start with cleaning your InDesign cache and preference.. Troubleshooting 101: Replace, or "trash" your InDesign preferences
If this does not work, upgrade to CC 2017.1 (latest) and let us know if it worked.
Thanks, I followed both of your instructions and I was able to open my file again. Unfortunately another problem appeared- when I try exporting as PDF file, another message appeared- 1 problem ( 1 failure) was found with a background task: export: "portfolio 1stjune.pdf (1)
PS. I am printing my portfolio in 2h
I am happy that finally InDesign worked for you.
I suggest you close this thread and start a new one for the new problem you are seeing now. This will enable other people also to add their responses and easy reference point in the future.