Panel installation errors - CentOS 5.3

[anvir]

All software was installed and configured as described in manual for CentOS, then I start "cd /var/www/ispcp/engine/setup && perl ./ispcp-setup", answer some questions, and got this:

Code:

...
        Possible values: [i]nfront, [b]ehind, [n]one. [none]:
        FastCGI Version: [f]cgid or fast[c]gi. [fcgid]:
        Activate AWStats. [no]:
        Starting Installation...
Can't exec "which": No such file or directory at ispcp-setup-methods.pl line 652.
Can't exec "which": No such file or directory at ispcp-setup-methods.pl line 653.
Use of uninitialized value in substitution (s///) at ispcp-setup-methods.pl line 655.
Use of uninitialized value in substitution (s///) at ispcp-setup-methods.pl line 656.
Use of uninitialized value in length at ispcp-setup-methods.pl line 658.
Use of uninitialized value in length at ispcp-setup-methods.pl line 658.
ERROR: Undefined template replacement data in repl_var: {RKHUNTER}!

Anyone knows what is it?