I doubt that xcopy is having memory problems. You need a really large number of files to get this error. Unless you use an old version of xcopy. Well do ya? :-)

In some cases when xcopy is used for making backups it makes a difference under what user the command is executed, for example if you access data on a mapped network drive (user System/Administrator/other) but in your case that’s (probably) also not relevant.

I think it could be something silly like a missing file (probably the file is there but not in the right place according to xcopy) or a file name that is too long so it bombs out with a "0x4". I would check from where the command is run, under what user and if the files are visible from that place.

Hope this helps

BTW Why do you build it yourself on Windows? Surely using prefab binaries is the easier solution;-)