The compiled binary of Autodock has some annoying limits, such as this or maximum 32 rotatable bonds. There's no other way to overcome it but to compile Autodock on your own (source code is free) and set these maximum values to larger values.
Upon downloading the source code you have to change the "MAX_ATOMS" value in the "constants.h" file from 32 to any desired number (I have a version with 64 MAX_ATOMS and it works fine).
Compiling is well described in the README file of the autodock suite and it depends in your machine, but I did the usual steps on my CENTOS (./configure, make, make install) and had no problems.