Anritsu MS2721A - Firmware update files

[pamphonica]

I've just got an Anritsu MS2721A (not the later 2721B) which is stuck at the boot (1.52) page, showing "Invalid OS Image".
Any MS2721 gurus out there?

I can set ethernet from the boot page menu.  I can even retrieve a new firmware package and perform an emergency reload of the firmware update, via the Anritsu MST package and ethernet connection on both devices.
But when the process (presumably successfully) completes, the device still re-boots into the boot page, not the main OS/application.
The CF card is there, and contains quite a lot of files (looking like the correct set, based on the release numbers).
But the CF contains only:
Firmware Update folder: text file confirming MS2721A and update v1.74
OS folder: Vxworks.bin
Sys folder: all the expected files in app/base/bmp/wav folders.
Usr folder: empty.
And when I examine the zip file downloaded by the MST app, it does not seem to include an OS.  But it does have a lot of other stuff, still the same versions as already on the CF.
When I examine the MST files list document, it shows that there is no executable zip file.
I finally tried copying the contents of the folders from the zip file downloaded by MST to the CF.  But once again nothing useful happens.
Could anyone let me have a copy of a working firmware files zip (OS1.52)?  Or even a previous OS version that will run?
many thanks
Jeremy

[pamphonica]

and the main boot menu page:

[pamphonica]

Ah - I had hoped that someone could help.
Is there no-one out there with a working 2721A that could have a look and see which files are there?
many thanks
Jeremy