The "project saved with future release of C3" message appears if you do something like save a project in r150 and then try to open it in r148. That's normal.
If you get a different error opening your project in the latest release then you can email it to firstname.lastname@example.org and I'll see if it can be recovered. However I must warn you:
- it's not always possible (it might be unrecoverable)
- you should keep regular backups anyway
- if a Construct bug caused a project corruption, we cannot fix the problem that did this (so it might happen again) unless we have a full bug report, including steps to reproduce etc.