The file is good, I use this updater on several machines as well as my own which all have the same issue, I am able to upload and even upgrade to this exact file using the web interface of the device in a browser without error. The device checksums the file before going ahead with a firmware flash, so it's definitely not corrupt on the disk.

Using wireshark the post never even appears (it does when using the web ui, and did using this script before), all I get is a 200 ok after attempting the post, with the error message that states "connection was interrupted, or the file is corrupt. As per the other reply I will try the LWP debug and see how that goes for finding more info."