Had you copied them there?
This is a common mistake made by people who think that it makes compiling easier. It may, in fact, make compiling easier -- but it wreaks havoc at run time.
To anyone reading this at a later date, there's one rule about the jar files that come with
Tomcat (or any other app server):
Leave them alone.
Don't delete them.
Don't move them.
Don't copy them.
Follow this rule and no one gets hurt!