java.lang.NoSuchMethodError: javax.servlet.ServletResponse.getContentType()

On windows XP when I start Tomcat 5.5.27 throught the eclipse plugin, and try to view a JSF app in a browser. When I start Tomcat at the command line it seems to be fine, but then I can’t use the Eclipse debugging features etc.

I guess Eclipse is including some innappropriate jar files in the classpath or something, but I’ve no idea where to look :(