This isn't the ideal way to run the tftp updater, since connecting the devices directly can cause the extra delay due to link setup / negotiation between the 2 devices to miss the short time window that the camera allows when waiting for a response to the UDP probe.
A PoE switch can also add extra delay and embarrass the tftp handshake.
The best chance of working is when both the PC and camera are each connected to a non-PoE switch or router port and the camera is powered separately using 12v.