I have already answered your other forum thread on a similar subject. For convenience I will paste my answer here as well:
The path to a specific file in FileExplorer is passed in the URL and the control uses a GenericHandler (.ashx file that handles the files) to decode the path before it is used (and the white spaces are not among the allowed URL characters). This is why you need to avoid the using of any reserved symbols (including #, ?, etc.) in the name of the files.
More detailed information is available in the following W3C article:
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