Posting in the Magento forums has been disabled pending the implementation of a new and improved forum solution which should better serve the community.
For new questions please post at magento.stackexchange.com, the community-run support site for the Magento community. We will be providing updates on the new forum solution soon. For questions or concerns please email firstname.lastname@example.org.
Your problem could be resulted from that some module on your site have called function in Helper file of Adminnotification but it has not found. You need to go to your back-end->System->Configuration->Advanced and check Mage_AdminNotification status. If Mage_AdminNotification status is Disable you need to change to Enable so that your site works normally.