You need to install all the dependencies as stated in that webpage before executing the install command.
BTW, are you using Ubuntu in the machine that you reports installation error?
Also, are you sure you get no error message when you install Calibre using apt-get on that machine? If yes, the problem may be that the ebook-convert program is not put into the search path for binary programs. You may first look for the "ebook-convert" program (see
here for details). Then call the program using its absolute path.