In all my years tiling I never came across this scenario.
I'm going to tile a bathroom (bathtub area) and upon removing the old tiles, i noticed that the green tape that comes with the drywall peeled off along with the tiles. Now the only thing left there is the brown cardboard type material.
I was wondering if I can proceed to tile with some adhesive 12x12 porcelain tiles on it? Or do I have to replace all the drywall?
Sound like the drywall has at some time had moisture issues, and the two just don't mix. I would rip it out, replace with cement board or Kerdi over new drywall, but maybe that's just me. The tile and your time is too much of an investment to not do it right.