The problem might be caused by your previously stored YouTube settings, which don't automatically change when you switch your location using ZenMate.
To fix this, scroll to the bottom of the YouTube page and change your country setting to "Worldwide" (see picture below) to visit the global version of YouTube. Afterwards, reload your page and your problem should be solved.
Please take note: Geo-restricted sites can use various data to recognize your real location such as IP tracking and if you've visited the site before, using cookies on your device. ZenMate allows you to bypass some of these methods by providing a different IP address in the corresponding country.
For accessing these sites with ZenMate there are some steps you can take. Make sure that you are using both the latest version of your browser and the latest ZenMate version. Moreover, please clear all browsing data including your browsing history, download history, cookies and cache (see browser settings). As an alternative, you can access the site by using your browser's privacy/incognito mode.
As a Premium user, you can also add these sites to your Smart locations to prevent this from happening in the future! To learn more about Smart locations please check out:
I want to use site specific ZenMate settings. How does Smart Locations work?