I had the same problem after updating ISPC from 220.127.116.11 to 18.104.22.168. The Reason that ISPC could not update the user table in mysql database was the change of password use. It seems, that ISPC since Version 3.0.4.x works with password hashes instead of clear text passwords.
After setting the passwor again, the update for remote access works fine.
// Regards Micha
ISPConfig 2.2.37 @ ubuntu 8.04 LTS (Apache, MySQL, Postfix, Courier, ClamAV, SpamAssassin)
ISPConfig 3.0.45 @ ubuntu 8.04 LTS (Apache, MySQL, Postfix, Dovecot, ClamAV, SpamAssassin)