Hi there,
First of all, please make sure that you are fully updated including X Theme and Plugins.
You can find the latest version numbers here: (https://community.theme.co/kb/version-compatibility/) Then you can compare them to what’s installed on your site.
If you find anything to be out of date, you can review our update guide.
Once you update your X theme & Cornerstone plugin, I advice you to revoke your license key and re-validate (revoke link can be found on the bottom of the X Addons section). Then you should be able to install our extensions properly.
Let us know if that helps.
Thanks!