Explanation of Issue
There are a couple of possibilities for this issue:
1. The show file in question has a large amount of data in it.
2. The SD card has a number of files (including non-SmartFade files) in the Root Directory
When reading and writing to SD cards, SmartFade creates a list of all of the files and folders in the Root Directory in its internal memory so it knows where to look for existing show files and what space is free to write new show files.