Migration from Flex 3 to Flex 4 Errors

Hello I migrated my Flex 3 project to FLex 4: I am getting these errors:

Anyone has an idea about fixing this in Flex 4.

1061: Call to a possibly undefined method activate through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method activate through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method activate through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method activate through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method addFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method addFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method addFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method addFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method removeFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method removeFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method removeFocusManager through a reference with static type mx.managers:ISystemManager.
1061: Call to a possibly undefined method removeFocusManager through a reference with static type mx.managers:ISystemManager.
1144: Interface method addPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl. 
1144: Interface method addPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl. 
1144: Interface method addPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl. 
1144: Interface method addPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl. 
1144: Interface method createPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl.  
1144: Interface method createPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl.  
1144: Interface method createPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signat开发者_JAVA技巧ure in class mx.managers:PopUpManagerImpl.  
1144: Interface method createPopUp in namespace mx.managers:IPopUpManager is implemented with an incompatible signature in class mx.managers:PopUpManagerImpl.  

Thanks for your help.

Errors like this are usually due to version mismatch issues. So, make sure that all your external libraries are compiled with the same version of the Flex SDK that your main project is.

If you are using frameworks, or other libraries you found on the web you may have to recompile them yourself if the source code is available.