[Cory Sanderson]

hi i also just got this error multiple times

and by googling the error message found your message

i downloaded the 3.5 plural eyes which also had an error with the file but instead it said had an unsupported format included in the xml file

i looked through my fcpx project and found that i had accidentally added a jpg still photo into the project

i removed the photo and re exported the xml file and whalla
back to normal

this may not be your solution but the error message that my accident caused was the exact error message you encountered so it might give you a hint to the cause

cheers