Actionscript Error: declaration must be contained within the <Declarations> tag, since it is not ass

Issue:

When you edit a actionscript, you may got followingerror.

Error:

declaration must be contained within the <Declarations> tag, since it is not assignable to the default property’s element type ‘mx.core.IVisualElement’.

Solution:

Please check if there is a typing mistaken in your code. Especially for a extra or unecessary letter.