Just posting an experience. Maybe this is a bug report.
Recently downloaded X-CTU from the web site (40002637_c.exe), then downloaded latest firmware versions through the X-CTU.
I was then able to upgrade a series 2.5 Pro module (XBP24-BWIT) from 2.5 Router AT to ZB Coordinator API, then to ZB Router API without any trouble. I followed the instructions provided, specifically had the “Always update firmware” checkbox ticked while "Write"ing parameters and firmware.
Then tried to upgrade a ZB Module (ZB24-Z7WIT) from ZB Router AT to ZB Coordinator API, and had repeated failures. The process would start, then the “Comms failure/please reset” dialog would appear. Unit remained accessible and usable … as a Router AT.
The programming finally succeeded when I unchecked the “Always update firmware” box.
So, I can’t explain the inconsistent behavior, but perhaps its worth noting.
[as a side note this was all done through my own home-made USB adaptor … essentially clones of the USB adaptors. Hopefully no hardware differences.]