Hello all.... I had the same problem above.
But, i have noted that the isp installation removed all the things in the folder install_ispconfig.
Then, i began to search, how and why the installation script removed all the files in the folder!!!
Before the last line of the script, i've found the command to delete all those files.
Then, i coment that $%#%$#% and after this, i can install this %$#%$# without errors!!!
That's it !!