At first i have to say that this is a very good modul.

There is an error on saving the activity: in the file bxActivitiesDb in line 170 is a qoute character too much respectively to little:

$this->query("INSERT INTO `" . $this->_sPrefix . "activity(`activity_id`,`lang_key`,`params`,`type`) VALUES ($iEntryId,'$sLangKey','$sParams','$sType')");

has to be

$this->query("INSERT INTO " . $this->_sPrefix . "activity(`activity_id`,`lang_key`,`params`,`type`) see more VALUES ($iEntryId,'$sLangKey','$sParams','$sType')");