by Paul Charsley.
Hi Jeff,
This can happen when a web service function defined in your Moodle database does not exist in your Moodle code. It may happen if you switch to an older source code branch but are still using a newer database. It is unlikely to be a bug.
When I encounter this error I usually check the functions listed in the table mdl_external_functions to verify that my Moodle installation contains the corresponding code.
Paul