It says I don't have enough space when moving file into external drive.?

It says I don't have enough space when moving file into external drive. But I have more 2gb more after moving the file. The single file is about 4gb but I have 6gb left. When I move other files this doesn't happen. Is this because the file is so big ? But that's too weird because it's in my... show more It says I don't have enough space when moving file into external drive. But I have more 2gb more after moving the file.

The single file is about 4gb but I have 6gb left.
When I move other files this doesn't happen.
Is this because the file is so big ? But that's too weird because
it's in my main drive.
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