Auth session invalid usually stems from network connection issues between you and the buddyauth servers. make sure your not running any applications or anything that could be bogging down your connection or causing issues.
no i'm not running anything on this PC beside wow and HB, no antivirus installed ..etc, its random, sometime its just 5 minute after i log in the bot, sometime 1 - 2 hours after login bot, i use 3x3 sessions on this PC, and its not happen at the same time to all session, just 1 session at the time ( random )