The reason that this error occurs is because the wrong file type is attempting to be uploaded to the PIX Firewall. The administrator is attempting to upload a pixNNN.exe file instead of the correct pixNNN.bin file.
Note: NNN represents the appropriate version of the software and is consistent in both file names.
The pixNNN.exe is a self-extracting file that contains the pixNNN.bin file. The correct procedure is to download the pixNNN.exe file to a location on the network. Then, double-click on the file to start the extraction. At that point, move the pixNNN.bin file to the root directory of the TFTP server. Once the copy is complete, it will be possible to upload the pixNNN.bin file to the PIX for an upgrade.