By trial and error I found my way how to give the frames a transparent background. I was testing 'speedo.wif' through 'speedo10.wif'. What I got was transparency for all the frames except the first one (speedo.wif) although I had it selected along with the other ones. I had to select it once more in addition in order to get the transparency. Is this a feature?

So in the end, it did work Inger?

Yes, after I had selected the first image twice.

Inger, can you email me the steps you took so I can try and replicate this here?