Calendar - popup reminders does not work

[funbsd1]

Popup reminders does not work.

I'm sure popup reminders are in "reminders" database table.

No error found in php_error_log/roundcube_log/firebug.

Do I have to change any parameter in config.inc.php?

I have deleted all plugins, except below:
calendar
filesystem_attachments
http_auth
jqueryui
jscolor
qtip

Firebug report below. Does that mean no reminder found in database?
GET http://localhost:8000/webmail/?_task=dummy&_action=plugin.calendar_get_reminders&_ts=1343148870610&_remote=1&_unlock=0&_=1343148870611
RESPOUND ..."callbacks":[["plugin.calendar_displayReminders",[false,[]]]]