I encountered the same error. My script brought a list of files from a unix server through the firewall then PUT the file(s) on an NT server. It failed on the PUT during the inbound session.
Process of elimination found the problem to be permissions set on the NT server when I was not allowed to delete existing data files. It would'nt allow duplicate data file names to be written either. For testing I had the script put the file with an added extension and it worked.