Samsung SR-S20DTD Freezer: whipe paperlike substance?

We have a problem with our Samsung SR-S20DTD fridge's freezer.

Over the last weeks it ws not staying very cold, and then the freezer temperature
display started blinking, indicating a freezing ventilation (or related) issue.

We found lots of ice at the vents, and apparently also behind the rear covers where the
ventilation ducts are.

We turned the whole system off and let it defrost.

I then found what looks like a while substance behind some of the vents.
Its consistency is like tissue paper which was frozen or had gotten wet and thawed/dried,
ie at once clumpy but also flaking

What is sthat stuff and how did it get there?

if it was some form of filter, I would expect there to be some procedure to change it
in the manual, but there is not.

Pictures:

https://dl.dropboxusercontent.com/u/...018.48.47a.jpg
https://dl.dropboxusercontent.com/u/...018.49.06a.jpg

Does anyone have any instructions how to dismantle the inner back wall of the freezer
to expose the ventilation ducts? there are a few scres holding the icemaker motor
etc in place, but the actual backwall seems to also be clipped into the back, and
while I havenoticed some small arrows (about 6) on either size pointing to what might
be clip points, I had no luch trying to unclip that.

Any help is appreciated

thanks
M