Traditional UNIX TFTP servers require that the file to upload is already existing and writeable on the TFTP server. The existing file will be overwritten by the upload.Typically, the UNIX utility "touch" is used to create an empty file. The empty file's permissions are then set with "chmod".
This obscure mechanism is still implemented in many TFTP servers on Linux systems, but not widely known any more.
The error message "Error: (1) File not found" is typical for this kind of problem.