Cause: Network instability, file too large, or browser timeout.
Solution: Use a direct Ethernet cable, clear your browser cache, or switch to a different browser (Firefox or Chrome, avoid older IE versions). Alternatively, use the TFTP method.

Cause: Power interruption or corrupt flash.
Solution: Perform a hard power cycle (disconnect power, wait 10 seconds, reconnect). If still unresponsive, attempt a recovery via serial console and TFTP.

Firmware files are often tied to specific hardware revisions. Check the label on the physical device. A mismatch between firmware and hardware revision can cause permanent failure.