(Copied from original User Voice forum)
"When there is an unknown node in the Maya scene file, and you wish to change the file from an MB to an MA file type, Maya currently gives an error saying it cant change the file type due to the unknown node...
Instead of giving the error (which many newbies may not know how to go about fixing), can't Maya just show a pop up box to delete the unknown node and save as the desired file type, or save as current file type instead?"