That usually indicates a conflict with another plug-in. Please check by turning off the other plugins one by one.
But you also mention adding a page> I do not see Power or Experience in your Plugin environment…
What page are you trying to add? Do you mean a WordPress Page or are you referring to activating SEO pages with the SLP Power add-on?
If WordPress, you will need to Troubleshoot with the version of WP you are using and see if others have reported that or if there is an issue with your server, etc.
You might want to also use the Debugger