Good day, I am having a problem regarding opening captivates projects, please advice in this.

In case you decide to upgrade your hardware in the future, you may wish to download the latest version of Adobe Captivate 11.8 to be sure when you reinstall your software in the future you don't have to go through the added steps of upgrading through all the versions to get up to date.

As Rod points out you need the same or a more recent version of Captivate to be able to open the project.

Moreover it could also still be locked on another system by another user. 

Is this file one that you have previously opened and edited or is it from someone else?

What version of Captivate are you using?  (Please give both the major AND minor version numbers. You can find that information in Captivate under the Help > About Adobe Captivate menu item.)

What version of Captivate was used to create or last edit the CPTX?  If your version is not the same or later than that, then this could be the reason you cannot open this file.  (The error message doesn't always give all the information you need.)