The majority of the diagnosis starts with the system log. This is the place where most of the applications in the platform display their warnings and errors, generating entries that can fall under these three levels: Information, Warning, or Error. You can view them all at System Logs > System Log > All. There are also modules for individual levels. Add the Created by field to the list to show which user generated the entry.
The system log can become pretty huge. Each of the modules contains a filter that only shows items that are
Created - on - Today. If you build your own filter, keep a date filter in place, even if it is modified.
The platform and applications will record any scripting or internal errors in the system ...