Selenium Remote Control (RC) is a test tool that allows you to write automated web application UI tests in many programming languages against any HTTP website using any mainstream JavaScript-enabled browser. Selenium RC is a powerful and simple framework for running (scheduled or manually) automated UI centric regression tests for web applications / services. Here are few simple tips for Selenium RC java client. I used JUnit for tests. You can use NGUnit too.

1. To run the Java client you need to only have selenium-java-client-driver.jar (located in selenium-remote-control-1.0-beta-1/selenium-java-client-driver-1.0-beta-1 ) in your classpath.

2. The automatically generated java file (from Selenium Core) is likely to be defective. Ensure at least you have the following import statements:

import com.thoughtworks.selenium.*;
import junit.framework.*;
import java.util.regex.Pattern;

3. Ensure that the saved file name matches the generated class file name.

4. Remove the package statement or replace it with your own package statement. Initially just remove it.

5. Error: java.lang.UnsupportedOperationException: Catch body broken: IOException from cmd=setContext&1=SeleniumSTSanityTest.testSimpleThoughts -> java.net.ConnectException: Connection refused

Have you run the Selenium server?
Run the Selenium server like this:
java -jar selenium-server.jar

The selenium server is located in:
selenium-remote-control-1.0-beta-1/selenium-server-1.0-beta-1

6. Error: com.thoughtworks.selenium.SeleniumException: ERROR Server Exception: sessionId should not be null; has this session been started yet?

Ensure that the browser is in the PATH before running the server. On my linux box I did:
export PATH=$PATH:/usr/lib/firefox-2.0.0.6/

7. Error: com.thoughtworks.selenium.SeleniumException: Permission denied to get property Location.href

This happens on Firefox when a previous page wasn't fully loaded before the next page was invoked (due to timeout or click() was used). The solution is to use *chrome instead of *firefox in setup. I use for firefox:
setUp("http://blog.taragana.com/", "*chrome");

8. Timeout error
Increase the time in selenium.waitForPageToLoad() to 60000 (1 minute) or more.

9. How to run the generated java Test file?
This is really a JUnit question but in short you can add the following code in the generated file to get it running:

public static Test suite() {
	return new TestSuite(SeleniumSTSanityTest.class);
}

public static void main(String args[]) {
	junit.textui.TestRunner.run(suite());
}

Note: Replace SeleniumSTSanityTest with the name of your Java source file (without the .java extension)