I am a basic user and sorry if I miss to state some important facts.
I have similar problem raised here and also in many other pages. First, I followed the guides by Herbert Schulz, didn't work for me.
Afterwards, completely uninstalled MacTex with all GUI Applications and distribution files, then re-installed MacTex. Still, didn't work.
I also updated TexShop and BibDesk, which are the softwares I use.
Moreover, run the Setup-2015 package at Applications/TeX folder.
However, still when I click to typeset, TexShop brings the following message:
/Library/TeX/texbin/pdflatex/simpdftex does not exist. TeXShop is a front end for TeX, but you also need a TeX distribution. Perhaps such a distribution was not installed or was removed during a system upgrade. If so, go to http : // tug . org / MacTeX and follow the instructions to (re)install MacTeX. A less likely possibility is that a tool path is incorrectly configured in TeXShop preferences. This can happen if you are using the macports or fink distributions.