XMLRPCServerProxy module not working (problem: Duplicate Groovy Libraries on classpath)

The XMLRPCServerProxy seems not to be working. Whenever one tries to call any remote method, it fails with a MissingPropertyException.

However, if I try to call serverProxy.invokeMethod directly, it works.

So, the following fails:

def server = new XMLRPCServerProxy('http://localhost:8069/xmlrpc/common')
def uid = server.login('terp', 'admin', 'admin')

while the following works:

def server = new XMLRPCServerProxy('http://localhost:8069/xmlrpc/common')
def uid = server.invokeMethod('login', ['terp', 'admin', 'admin'])