OK had the exact same error message with iDisk upon startup on my iMac. Drive me crazy for 3 years !!!
Your post gave me hints. Went into System Preferences-Users&Groups-Login Items for my account (Admin one) and removed all items that had a Yellow Warning triangle (even those that were checked). Restarted my iMac and guess what: it's finally gone. All apps work fine so far. Just make sure you have a backup of your machine before doing that, you never know. THANK YOU !!!