Ok, I found some instructions from a while ago. This should help you get the issue fixed, but it depends which version you’re running. If you’re running the latest version then it will work.
Also, this link is a thread for the Epik theme, but it should still work for Optimal as well – https://appfinite.com/topic/portfolio-problem/#post-8091
Make sure and use FTP to edit your files instead of the WordPress editor just in case there is an error made anywhere (since this is dealing with PHP code).