# Why FileExistsQ gives False to some file full paths, which however, are given by FileNames? [duplicate]

I am working on a badly structured directory with *.nii files. First I use

dir = NotebookDirectory[] <> "ADNI";
fileNameList = FileNames["*.nii", dir, Infinity];


to get all the full paths, which works well.

The strange thing happens when I try to import them from the generated full paths and I am informed that some files can not be found.

So I make a test

Partition[Boole[FileExistsQ /@ fileNameList], 29] // ArrayPlot


and get (black for True, white for False)

Some examples from fileNameList are

{"F:\\Research\\Machine_Learning\\Alzheimer_Disease\\Dataset\\
I119626.nii",
"F:\\Research\\Machine_Learning\\Alzheimer_Disease\\Dataset\\
I36969.nii",
"F:\\Research\\Machine_Learning\\Alzheimer_Disease\\Dataset\\
20070731162014912_S23188_I63332.nii",
"F:\\Research\\Machine_Learning
MPR____N3__Scaled_Br_20070711170922052_S25016_I59224.nii"}


and examples that tested by FileExistsQ for True and False, respectively, are

{"F:\\Research\\Machine_Learning\\Alzheimer_Disease\\Dataset\\