No technical expert advice can be found here ;)

Missing required argument ‘module[s]‘
Google Web Toolkit 2.0.3
DevMode [-noserver] [-port port-number | "auto"] [-whitelist whitelist-string] [-blacklist blacklist-string] [-logdir directory] [-logLevel level] [-gen dir] [-bindAddress host-name-or-address] [-codeServerPort port-number | "auto"] [-server servletContainerLauncher[:args]] [-startupUrl url] [-war dir] [-extra dir] [-workDir dir] module[s]

where
-noserver Prevents the embedded web server from running
-port Specifies the TCP port for the embedded web server (defaults to 8888)
-whitelist Allows the user to browse URLs that match the specified regexes (comma or space separated)
-blacklist Prevents the user browsing URLs that match the specified regexes (comma or space separated)
-logdir Logs to a file in the given directory, as well as graphically
-logLevel The level of logging detail: ERROR, WARN, INFO, TRACE, DEBUG, SPAM, or ALL
-gen Debugging: causes normally-transient generated types to be saved in the specified directory
-bindAddress Specifies the bind address for the code server and web server (defaults to 127.0.0.1)
-codeServerPort Specifies the TCP port for the code server (defaults to 9997)
-server Specify a different embedded web server to run (must implement ServletContainerLauncher)
-startupUrl Automatically launches the specified URL
-war The directory into which deployable output files will be written (defaults to ‘war’)
-extra The directory into which extra files, not intended for deployment, will be written
-workDir The compiler’s working directory for internal use (must be writeable; defaults to a system temp dir)
and
module[s] Specifies the name(s) of the module(s) to host

After working for a little while with GWT in eclipse, the project can not be run any more as “GWT application”. I’m still about to figure out what  is happening. In the meanwhile I want to give you a simple and quick workaround for the problem:

1) Select “Run Configurations …” from you “Run” menu in eclipse

2) Delete the configurations of your project under “GWT Application” and “Web Application”

That’s it. Now you can again run your project from the selector and Jetty will start without any problems.