I was in a middle of working on a project and tried to understand key frames since I am new to this program.
I tried to click on the add\remove key frame to do some changes and then premier crashed. When I tried to reopen the project, I got this message "This project contained a sequence that could not be opened. No sequence preview preset file or codec could be associated with this sequence type."

Since then I am not able to reopen the project that I have been working for the past week.
Please help.

Try opening one of your auto-saves, if enabled. Pick the one with the latest time stamp, not the highest number in the file name.

If that doesn't work you might try importing your old project into a new one. That sometimes used to work.

Thank you Adam for taking the time.
I ave tried what you suggested and I am getting the same error message.
I really don't want to believe that it is gone for good.

I was able to fix it by uninstall it and then use the adobe clean up tool and re-install.
I am so happyyyyy

That's great news, and good to know for future reference.