When requesting a user's details via the core_user_get_users_by_id function Moodle throws an exception if the user's timezone is UTC+10 or higher. Setting the user's timezone to a lower value or Server's local time makes the API function work again. I have tested this in an empty Moodle 2.3.2 setup, so I do not believe it's configuration related.

The error returned is the following:

<?xml version="1.0" encoding="UTF-8" ?>
<EXCEPTION class="invalid_response_exception">
<ERRORCODE>invalidresponse</ERRORCODE>
<MESSAGE>Invalid response value detected</MESSAGE>
<DEBUGINFO>timezone => Invalid response value detected: Invalid external api response: the value is "10.0", the server was expecting "timezone" type</DEBUGINFO>
</EXCEPTION>

Please let me know if you require further information.