Hello,
might be an old one, but this error message seams to lead to so many different individual reasons:
In my case (Canon EOS 5D Mark3) it was the setting (in the German Manual it's on page 146): "Rauschreduzierung bei Langzeitbelichtung" (Noise reduction on long exposures), which is a setting that is, if enabled, is applied to exposures longer then 60s. If it's turned on, then INDI can't download the images.
It took me 2 years to find that out... but it was actually this thread that led me to go after settings concerning long exposures...
To save some similar troubles to other DSLR users, maybe there should (if not already and I am simply blind) be some notes in the driver documentation, that to prevent that errors, any DSLRs setting, that does some internal image processing on long exposures should be turned off, as this might break the connectivity to INDI.

regards,
Felix

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