Do you have maven 2 also installed?
I found one link in searching, see if it helps
http://blogs.oracle.com/sreekanth/entry/java_lang_noclassdeffounderror_org_codehaus
and also double check your environment variables to make sure you have set all the variables mentioned in the doc.
For this error "mvn is not recognized as an internal or external command", add src/bin folder in 'path' environment variable.
