I noticed that you've actually posted to several other sites with the same question. Hope my answer could calm you down somewhat.
I'd suspect it is a classpath problem. As my eclipse is currently giving me some problem, I could not check if I have a classpath for servlet-api.jar or the like.
If you're in desperation (judging from the numerous sites you've posted the question, I think you are), why not add all apparent servlet jars such as servlet-api.jar from \\[jboss-4]\server\all\deploy\jbossweb-tomcat50.sar to your project classpath?
When things regain normalcy, then you could use binary elimination to elimate those jar files that have no effect ?
Caveat: Just make sure that you don't include jar files of duplicate packages that belongs to different versions. I made that mistake once, and it was very painful.
Originally posted by Yu Tao: Hi I'm not sure if this is the correct place to post this, but I've seen the same problem posted elsewhere on the web and seen it left unresolved.
This is the error I get when I try just to instansiate ( DiskFileUpload d = new DiskFileUpload() ),
I've tried almost everything with it, please help!! ( ps: I'm using eclipse and jboss4, I'm pretty sure my classpaths are ok - I put the commons jar into the shared lib folder of jboss )