macvim can not fold code "E490: No fold found"

Your .vimrc doesn't actually enable folding anywhere. Folding is not enabled by default. You need to tell Vim what method to use to fold your code.

What method you use might depend on what type of code you are editing. SOME syntax highlighting files define syntax-based folding. Other syntax files do not. If your code is of a type that supports syntax-based folding, then you can :setlocal foldmethod=syntax after loading the file. You can do this in an autocmd in your .vimrc if you like, for example autocmd FileType c setlocal foldmethod=syntax or you can do it manually.

Other automatic fold methods include "marker", "expr", and "indent". By default the fold method is "manual" and you must first create folds with zf in order to use folding commands.

See http://vim.wikia.com/wiki/Folding for a more detailed discussion.