permissions / owner / chmod

hi there
i have still a little problem with my guestbook-script (but i'm getting better i'd say... ).
i get an internal server error. in my error-log is this message:

[client 1XX.XXX.XXX.X] file permissions deny server execution: /usr/local/virtual-web/XXX/htbin/guestbook

(my browser says: "file not found", not very helpful i'd say...)

i see in my ftp, the script is "owned" by me, not by "nobody", is that the problem? if yes, how can i change the owner (chmod?)?

ok, thank you a lot for your help!!