Here is the updated procedure for installing NBO 5.9 for Gaussian09:

1. Rename the files l607.F and l607.a in the Gaussian executable
directory to l607.F.old and l607.a.old, respectively.

2. Enable the g09 version of the NBO program using the 'enable' program
that is provided with the NBO distribution, following the general
instructions in Section A.2 of the NBO manual. Copy the file g09nbo.f to
the Gaussian executable directory and rename it l607.F

3. Prepare the updated l607.exe executable by compiling l607.F and
linking it with the Gaussian utility libraries. In most cases this is
accomplished by issuing the following commands:
$ /bin/csh                (Change to C-Shell)
$ cd $g09root/g09         (Move to the source directory)
$ source bsd/g09.login    (Source the g09 environment variables)
$ mg l607.exe             (compile l607.exe using the mg alias)

4. Set the permissions on the newly compiled l607.exe file with the 
following command:

$ chmod 750 l607.exe