Magento 1.9.2.1 has just started throwing the exception
'Mage_Core_Exception' with message 'Mage registry key "_singleton/admin/session" already exists'
it happens with different cron jobs - if I disable the extensions relating to the cron that triggers the error, then the error happens on a different cron job, but not all cron jobs.
Some of the cronjobs that trigger the error are successful after the 8th or 10th run.
I've spent the day googling and all i can find is reference to the compiler and clearing the cache - I've cleared the cache about a million times and the compiler has never been switched on - i've cleared it and run compiler --disable to be sure.
I'm absolutely stumped and would appreciate some help.
full exception here
Cron error while executing core_email_queue_send_all:
exception 'Mage_Core_Exception' with message 'Mage registry key "_singleton/admin/session" already exists' in /home/user/public_html/app/Mage.php:595
Stack trace:
#0 /home/user/public_html/app/Mage.php(223): Mage::throwException('Mage registry k...')
#1 /home/user/public_html/app/Mage.php(477): Mage::register('_singleton/admi...', Object(Mage_Admin_Model_Session))
#2 /home/user/public_html/app/code/community/Aoe/Scheduler/Model/Schedule.php(546): Mage::getSingleton('admin/session')
#3 /home/user/public_html/app/code/core/Mage/Core/Model/Abstract.php(316): Aoe_Scheduler_Model_Schedule->_beforeSave()
#4 /home/user/public_html/app/code/community/Aoe/Scheduler/Model/Schedule.php(196): Mage_Core_Model_Abstract->save()
#5 /home/user/public_html/app/code/community/Aoe/Scheduler/Model/Schedule.php(609): Aoe_Scheduler_Model_Schedule->runNow(true)
#6 /home/user/public_html/app/code/community/Aoe/Scheduler/Model/Observer.php(39): Aoe_Scheduler_Model_Schedule->process()
#7 /home/user/public_html/app/code/core/Mage/Core/Model/App.php(1358): Aoe_Scheduler_Model_Observer->dispatch(Object(Varien_Event_Observer))
#8 /home/user/public_html/app/code/core/Mage/Core/Model/App.php(1337): Mage_Core_Model_App->_callObserverMethod(Object(Aoe_Scheduler_Model_Observer), 'dispatch', Object(Varien_Event_Observer))
#9 /home/user/public_html/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('default', Array)
#10 /home/user/public_html/cron.php(77): Mage::dispatchEvent('default')
#11 {main}