Windows NT NFS products map permissions between NT and UNIX systems, but they don't adjust for the case differences between NT and UNIX file names.
When you save a file on an NTFS disk, the file is stored using the exact case you specify. Thus, if you save a file as MyFile.Txt, under NT, accessing this file as MyFile.Txt or myfile.txt (or any combination of upper- and lowercase letters) always produces the correct file because NT always converts the filename to uppercase when it searches for a file.
UNIX systems, in contrast, are case sensitive. If you try to access MYFILE.TXT on a UNIX system over an NFS link, NFS will report that the file is not found. This confusion happens because UNIX attempts to match the filename exactly as you specify. NFS server products on NT do not map filenames to uppercase. Thus, when you access a UNIX file from an NT system, be sure to specify the exact file name, otherwise your request will fail.