This is not an easy question to answer as several things can go wrong. Can be the wrong type of paper even if it is 140lb. Different manufacturers have different hardness and softness to the paper. Softness - meaning the fibers are not sufficiently compresses and bonded to each other. The paper could still have been a bit too wet - being a thick paper it could have soaked up a lot of water and although dry to the touch was still just wet enough for the masking fluid to take the paper with it. Overheating the masking fluid could be another - rather let the masking fluid dry and cool down before taking it off. Another point is that if masking fluid is applied too thickly it also can take quite a time to dry.
I'm so glad you didn't let that little bump in the road discourage you. I went through a rather 'tacky' stage a few months back and Nolan & Dennis pulled me through. Lillian is a great confidence booster...in fact I'm going to get her a brand new set of pom-poms! Where would we be without her?