MYSQL Fehler!

[der Flo(h)]

Schau dir mal an was

print ("SELECT user.id AS USER_ID, user.username AS USER_USERNAME, user.userpass, user.usertask, usertask.id, usertask.description AS USERTASK_DESCRIPTION FROM cms_user AS user LEFT JOIN cms_usertask AS usertask ON user.usertask = usertask.id WHERE user.status = 1 AND user.username = ".$username." AND user.userpass = ".$userpass."");

so ausgibt, und vergleich das mit deinen Spalten in der Datenbank, dann wirst du den Fehler schnell finden!