No.
There is no "too big" for Anatella! :lol:
Anatella can even create excel files that contains billions of rows (that excel won't be able to read because it's too big but other tools continue to read them).
I think that, here, the problems comes from another process that's locking the file. Typically, this means that the .xlsx file is already opened inside MS-Excel and MS-Excel prevents any other tool to overwrite the file. Solution: Just close the .xlsx file in Excel.
See you!