You have probably switched servlet containers by mistake.
is definitely a 2.3-ism and would generate an error in a 2.2 container :
Tomcat3/Jetty3 - servlet 2.2/jsp 1.1
Catalina/Jetty4 - servlet 2.3/jsp 1.2
You must have been running with a 2.3 container and move to a 2.2 one.
Hope that helps,
The only currently available package with jetty4 is the JBoss3beta which contains Jetty implicitly.