It tries to convert the path to the file into a "short file name", i.e., drive letter, colon, backslash, and 8.3 file names. It does this because the command line to the "download.c" code is space-delimited and won't take long file names. If it's on a network share that doesn't have an assigned drive letter (it's being accessed with the UNC beginning with a double back slash), the short filename conversion won't work. Are you sure it was because the network share was read-only, or was it because you mapped a drive letter to that network share at some point and it worked after that?