The file name(s) would be too long for the destination folder.
Windows under the hood supports pathnames up to 32000 characters however due to some reasons - which I can only think are legacy support related - programs like 'Explorer' will choke on anything longer then about 260 characters during copy operations. This is very frustrating and can be major pain if you are re-installing your system and are keeping your program settings for example the Eclipse Workspace folder.
In my quest for a solution I have found Terra Nova copy but my experience found it buggy - eventually I have discovered FastCopy utility by a Japanese programmer - it has nice right click integration and works well with Windows 8.1 even though has not been updated in a while.
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