A lot of times you come across an error “Server Error in ‘/’ Application” while working on an ASP.NET application. This is a generic error and it occurs when code throws an unhandled exception occurs in an ASP.NET application.

Resolution
Here are some steps you can take to resolve Server Error in ‘/’ Application error:
Check the error message: The error message will usually provide some information about what went wrong.
Explore and investigate in the stack trace. Stack trace helps you to pinpoint the error and their location
Enable detailed error messages: By default, ASP.NET is configured to display generic error messages. You can enable detailed error messages by modifying the web.config file. Find the <system.web> section in the file and set the customErrors mode to “Off” like this: This will display detailed error messages that can help you identify the problem
<configuration>
<system.web>
<customErrors mode="Off" />
</system.web>
Review your code for any syntax errors or logical errors that could be causing the problem
Check error logs on the web server. Normally server logs hold additional information to resolve Server Error in ‘/’ Application error. Error logs give a lot of information on the location and description of the error. It will be easier to resolve them.
Rebuild and redeploy your application: If you have made changes to your application, rebuild and redeploy your application to the web server.
Check your database connection: If your application uses a database, check that the connection string is correct and that the database is accessible.
Using the above steps you will be able to resolve Server Error in ‘/’ Application error in your ASP.NET MVC application.