Cannot access type in base class

I have the following base class:

================== Base.h ====================================

#ifndef BASE_H
#define BASE_H

#include <vector>
#include "MyType.h"

class Base {
public:

   // Types
   // We use pointers for polymorphic support.
   typedef std::vector<MyType*> ContainerType;

   // Pure virtual
   virtual ContainerType createJobs() = 0;

protected:
   ContainerType jobs;

};

#endif // BASE_H

================== Sub.h ====================================

#ifndef SUB_H
#define SUB_H

#include "Base.h"

class Sub : public Base {
public:
   // Types
   //typedef typename Base::ContainerType ContainerType;

   // Type from base class
   ContainerType createJobs();

};

#endif // SUB_H

================== Sub.cpp ====================================
#include "Sub.h"

   ContainerType Sub::createJobs() {
      // Create some jobs and add to parent container
     return this->jobs;

   }

================== End ====================================

The above does not compile:

     Sub.cpp:12: error: ?ContainerType? does not name a type

I have tried to typedef the type in the Sub.h:

   typedef typename Base::ContainerType ContainerType;

but that does not help. Why is it not possible to use a type defined in the parent class?