OCl project endeavors to maintain compatiobility beyond the latest release, so when Luna moved to ASM 5, there was a problem supporting installation on Juno and Kepler where only ASM 3 were available. Either the codegen.asm3 or codegen.asm5 plugin is used on the relevant platforms.
If you create a Luna installation, ASM 5 is installed and ASM 3 is missing, so you get compiler errors. Unfortuntately Luna does not allow you to directly install ASM 3 from Orbit http://download.eclipse.org/tools/orbit/downloads/ to remedy the deficiency.
If you are very astute, you will install ASM 3 before you install ASM 5, but more likely it’s too late, so copy or install e.g. org.objectweb.asm_3.3.1.v201105211655.jar somewhere and then copy it to the installation dropins folder. Restart Eclipse and the errors go away.