What does it mean: The file doesn't contain exactly what SL believes it should contain. CRC is a hashing function. Given equal input files, CRC outputs the same hex string. Two files with different CRC are guaranteed to be different. Two files with equal CRC are probably equal.
Why is the file different: Lemmini loves to eat or mutilate your files, then complain they're different. We've criticized that. Allegedly, SL has improved on Lemmini's voracity. Maybe SL is still not perfect at leaving data alone, or maybe your disk has bit rot.
What you should do: Hunt for a copy of whatever SL expects, and replace your file with that. Keep SL up to date.
-- Simon