The WebSphere Portal Test environment is a great place to run and test portlets, but it is finiky.
SOmetimes if the test environment has hot method replace enabled, it will fail. You might want to disable this. Also, make sure you are pointing to the right server in the Windows-Properties section of the server configuration. It's been a while since I configured the server, but I recall you have to point to a stub or something.
I have a bunch of tutorials on how to create WebSphere Portlets here: