unable to build using jdk1.4

Looks like a thirdparty lib was built using jdk 1.5 Builds fine with jdk1.5 Matt xwiki: [javac] Compiling 422 source files to /Users/conway/Documents/ eclipse/workspace/xwiki/build/classes [javac] /Users/conway/Documents/eclipse/workspace/xwiki/src/main/ java/com/xpn/xwiki/XWiki.java:84: cannot access org.exoplatform.container.RootContainer [javac] bad class file: /Users/conway/Documents/eclipse/ workspace/xwiki/lib/exo-platform.container-2.0.jar(org/exoplatform/ container/RootContainer.class) [javac] class file has wrong version 49.0, should be 48.0 [javac] Please remove or make sure it appears in the correct subdirectory of the classpath. [javac] import org.exoplatform.container.RootContainer; [javac] ^ [javac] 1 error