Apachie2 log shows: sudo: no tty present and no askpass program specified

[mucsb]

The PiRelay does not work...However there is no error message displayed. Checking the apachie log file I found this message as I refresh the page:

**sudo: no tty present and no askpass program specified

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

#1) Respect the privacy of others.
#2) Think before you type.
#3) With great power comes great responsibility.**

I guess the PHP exec's sudo command asks for su password. Do you have an advise how could I fix this?
Cheers, Béla from Hungary.