I have older activities that are inaccessible and I get this error return.
That appears to be an issue with your data.
Contact Xert Support at support@xertonline.com.
Server errors like that are always frustrating, especially when you’re just trying to get a workout in. Usually, it’s just a temporary hiccup on the backend, but I’ve found that a quick logout and login often clears out any stale session data that might be causing the hang-up. If it’s still acting up, it’s worth checking if there’s an update available for the app or trying a different browser if you’re on the web version. Sometimes clearing the cache/cookies for the site does the trick too.