On Tomcat 6, I understand there are 2 possible mistakes:
1) declaring a first level dependency to javax.el:el-api:2.2.4 (or another version number)

Yes, although this really is independent from Hibernate Validator. Tomcat already has an EL implementation, so you never should have to add them.

2) declaring the hibernate-validator dependency without the exclusions (because one should always exclude those dependencies when using Tomcat 6).

Right, ideally this exclusion shouldn't really be required, though. Actually I was wrong yesterday, runtime dependencies are copied to WEB-INF/lib (provided scoped dependencies are not) so I think problem also exists when building a WAR and deploying that on a standalone instance.

May be you could add something about that on the ref doc? I wouldn't be surprised if a lot of people make the same mistake.

I'll check the docs.

@Hardy Ferentschik: Hardy, I remember we changed the scope for the EL impl from "provided" to "runtime" a while ago. Do you remember the motivation for this? In hindsight I think "provided" was actually better, since it avoids this sort of problem, i.e. HV will never pull in the EL dependencies.

Cheers,
Michael.

Thanks for the report and your feedback, Michael. It's much appreciated