1. Which line in your snippet is line 153? 2. Which variable is null? If you can't step through with a debugger, you can always use lots of 'if (blah == null)' everywhere, including stuff like 'if (clientGUI.getCustomerText() == null)'. 3. Finally, were you loading any additional classes or source files in your application?
Usually if something runs in eclipse, but not on the command line, it is a classpath issue. The program can't find some needed file or jar. Although with a NullPointerException that may not be right unless you are getting an object from some factory.