Composer autoloader not found. please run "composer install"(version - 7.11.15)

Hi,

Actually I have already installed 7.11.18 version on my another server folder. which also has errors
(Uncaught ReferenceError: tinyMCE is not defined)
so I have decided to hit a try on lower stable version which 7.11.15
But unfortunately, this version also giving me error.
Tell me what to do…
Thanks…