Removing old contact adhesive from wall

I want to redecorate the walls in my dining room but the previous owner has glued plywood with an imitation wood facing to the walls using contact adhesive.
Now it is very easy to remove the plywood panels but it leaves old contact adhesive on the plaster surface.
I can't paint over this because it is just too rough, with the swirl marks from the adhesive comb showing through. The adhesive won't scrape off and it won't sand.
Any ideas how to deal with this problem?

Only course here is to get a plasterer to skim the lot.. If it's just a few ,anagable blobs you could scrape off the adhesive with an old wood chisel, which will damage the plaster, fill the damaged area's with easifill. You probably will need to line too depending how good the prep is before painting.

Good luck