In another question a user mentions that many drivers in Windows impose a limit of 2^23-1 files for ntfs.
Max files per directory on NTFS vol vs FAT32
Is this correct? I can't find any other references to this, however I am empirically running into corruption issues with around 10 million files.
EDIT: Fyi- my files are in reasonably sized subdirectories (none with more than a few thousand files). The problem arises somewhat consistently when I unrar an archive of millions of smallish files.