That ‘allround’ error can be due to multiple cause which is a pity. Some possibilities:

• The former session with that project was not closed properly. You can check the folder where the project is saved and look out for extra file with extension .lck You can safely delete that ‘lock’ file.
• You are trying to open a project which was created in a more recent version which is not compatible with your version installed.
• The project has become corrupted. Can you open the backup file which normally has been created automatically when opening the project in a previous version.
• Captivate has become corrupted. You need to clean the Preferences.  Close Captivate and find the subfolder ‘utils’ under the installation folder. Run ‘CleanPreferences…’ and restart Captivate.
• Cache has become too big. Use the button ‘Clear Cache’ under Preferences, General Settings. That menu is available from the Welcome screen.

More details about troubleshooting under:

https://blog.lilybiri.com/tips-for-troubleshooting