Thank you. Deleting the zero length image allowed LimeUtil --update to work. Got successful programming, however, the version numbers did not change so I suspect the board was already up-to-date. Having done this there is no change to the issue, so it seems running all the latest software/firmware does not help.
I notice these errors in the output (they appear in both the working and non-working cases) - do these mean anything?
Tune Rx Filter: MCU error 2 (CGEN tune failed)
Rx calibration: MCU error 5 (Loopback signal weak: not connected/insufficient gain?)
In an attempt to research further I found this thread (Calibration Error [Fixed] - #5 by ricardas), so I played around with LimeSuiteGUI to see if I could reproduce the issue and try different CSW_VCO_CGEN and Scales VCO bias current values. I could not cause any error in the GUI, no matter what I try it always seems to work. This seems to suggest there is no hardware issue. If so, why the MCU errors above? If gain is an issue how can I determine the correct values? If not, then what else can I try? Are there any other diagnostics I can run?
Many thanks.