It is known that in Windows mega uses the fileSystem API, which basically writes the file to a sandboxed section of your local file system: AppData\Local\Google\Chrome\User Data\Default\File System\ ...
So, I had ~3GB free on my local disk and I tried to download a 2GB file. It failed because it said I ran out of disk space. My disk still shows that I have about 400MB free. According to this post ...