Exception ‘Mage_Core_Exception’ with message ‘Invalid callback:

Exception ‘Mage_Core_Exception’ with message ‘Invalid callback:

This Error Occurs when company_module name is invalid and not added properly in model tab in cron.

    
        
            1.0.0
        
    

    
        
            
                Yourcompany_Yourmodule_Model_Observer
            
        
    

    
        
            
                
                    */15 * * * *
                
                
                    Yourmodule/observer::updateAll
                
            
        
    

Change it to the

 
        
            
                
                    */15 * * * *
                
                
                     yourcompany_yourmodule/observer::updateAll