If possible, access the full error details. Often, ASP.NET error pages have specific information on the issue, such as a stack trace or error code. Enable custom errors in your web.config file to see detailed error messages locally:
<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>
Since your application is using Azure SQL Database, verify that the database connection string in your application is correct. Check if any recent changes were made to the database credentials or if the firewall rules on Azure SQL Database have changed.
You can use PowerShell to test connectivity and troubleshoot any VM or SQL Database configurations. For example:
Test-NetConnection -ComputerName "your_sql_server.database.windows.net" -Port 1433