Sometimes, if there are cascading popup’s which uses same object, then when you cancel the object is not available any more to be used on the other page. Which returns these type of errors.
Use conditions, like if the object is not empty, which will avoid these sort of issues on cascading popup’s.
Probably the object which is tried to roll back, doesn't exist anymore. Did you have a editable fields before pressing cancel? Otherwise you ‘forgot’ to pass an object along to the page, and then cancelling changes is not possible.