java.lang.ClassNotFoundException: org.apache.catalina.users. MemoryUserDatabaseFactory

This error occurs when the specified class "org.apache.catalina.users.MemoryUserDatabaseFactory" is not found in the classpath of the application.

To resolve this issue, you can try the following steps:

1. Check if the required jar file containing the class is present in the classpath. If not, add it to the classpath.

2. Check if there are any conflicting jar files that may be causing the issue. Remove any conflicting jar files.

3. Check if the class name is correct and there are no typos in the code.

4. If you are using an IDE like Eclipse or IntelliJ, try cleaning and rebuilding the project.

5. If none of the above steps work, try upgrading the version of the Apache Tomcat server or the library containing the class.