The meaning or possible cause of "invalid method hash" exceptions is a somewhat frequently-asked RMI question-- it may not be clear that it means that the client side tried to invoke a remote method (with a given name and descriptor) that the server side does not believe exists on the remote object. This exception detail message should be enhanced to better convey that meaning.

See also the following RMI-USERS threads:

http://archives.java.sun.com/cgi-bin/wa?A2=ind0111&L=rmi-users&P=5807
http://archives.java.sun.com/cgi-bin/wa?A2=ind0306&L=rmi-users&P=320