weigth paint does not paint

the problem: i have a mesh (horse) with a multires modifier on. i have made an armature for the horse, and put an armature modifier on the horse, put object to “armature”, bind to “vertex groups” and “bone envelops”… now when i pose the armature, it works pretty well, however i need on some areas paint weight for better fllow the bones.

so while still in pose mode of the armature, i click the horse, and immediately go into weight paint mode. the horse turns blue as it should. now i select the bone in question and paint, with mix strength 1, or with add strength 1. i know it should turn red, but nothing happens…

i am confused, i have done this before, but this time i cannot get any weights paint there. what am i missing? please help.

Show us your blend file

ah, not neccessary i just found my mistake! i had the “mask” button clicked, now i unclicked and it paints… thanks!