Add User to moodle gives XML-RPC Error (404): Unknown error

Hi,

When i check user and click on add to moodle button from joomdle user tab, it gives XML-RPC Error (404): Unknown error on a blank page and the user is not able to sync. But some other user not gives the error they synced properly without any error. The error generating user is not exist in moodle i have checked it.
Joomla version 3.X
Moodle 2.5

Thanks in advance.

Enable debugging in moodle to get more info about the error.

Thanks it helped me to resolved the problem