Having an error when trying to open a captivate file

This error message appears a lot of times for all kind of reasons, not always what you are reading there. It can also indicate a corrupted file.

You can check if there is no lck file somewhere, that is indeed locking the file. It will not be to only possible cause. I hope you have activated the backup, can you find the backup file, change its extension to cptx and try to open it?

Do not clear the cache, if you can identify which cache folder is corresponding with this project, it could help you to create a former backup by zipping that folder and renaming the extension to cptx.

You can try to clean the Preferences.