when do we get an error occured please contact system admin?

When I tend to make changes, publish the app and then run it locally, the web app runs FINE on local PC. Though, the native app on my MOBILE gives certain errors. Buttons that save data or change data giving the above error. Other simple on click buttons to open a page WORK.
1 answers

This is the generic error that you get when something goes wrong but there is no proper error handling implemented. If this is a native app you might want to enable logging to pinpoint the cause by following the instructions on: https://docs.mendix.com/refguide/mobile/building-efficient-mobile-apps/logging/

If it is a online app that you open on your phone inspect the logs for the error that leads to the generic error that is shown to the user.