Hi - thanks for the quick response.
Well, I followed the instructions in the Autodesk knowledge instructions and selected the first in the sequence and it automatically produced the IFL, which is in the same folder. I think the viewport animation would not work otherwise (?)Note that I also tried other filetypes before - including AVI and MP4 with same result; works in viewport, but not in render.
I am using Arnold renderer, with the parameters set to use Arnold Compliant mode and GPU...
However, after you sent your email I looked into trying to use the IFL file directly as the map. It wasn't an option using the OSL Bitmap Lookup that I have been always using, but it did load with the older Bitmap (which I normally avoid due to Arnold complaining sometimes). So that did work (yay!) - which is interesting, as this is not a method listed in the documentation and requires the older Bitmap widget - unless there's a way to get the OSL one to work.