Here is what I found on the topic in a forum:
"Currently the RPC link will only work with a queXS installation (that
has a modified version of Limesurvey in it) therefore it won't work
with the limesurvey hosted service. You can have a look at the queXS
limesurvey code though if you would like to backport the change to
your own Limesurvey installation. Once the new version of Limesurvey
has the XMLRPC system implemented I'll make sure they work nicely
together."
see
sourceforge.net/mailarchive/message.php?msg_id=28930033
You might ask if it goes ahead as planned...RPC seems to be implemented now in limesurvey. Would appreciate if you reported back here, if you hear something...
regards
M