Error on building Android app with sh-script

Hi, I try to run a shell-script to build an android application on my linux system. The script will be started froma php-file. I tested my script from my server console and it worked fine, just as i want... Now i try to start it from my php-script and i get following message in my log-file:

path.js:360
        throw new TypeError('Arguments to path.join must be strings');
              ^
TypeError: Arguments to path.join must be strings
    at path.js:360:15
    at Array.filter (native)
    at exports.join (path.js:358:36)
    at /usr/lib/node_modules/titanium/lib/titanium.js:43:28
    at Object.<anonymous> (/usr/lib/node_modules/titanium/lib/titanium.js:80:2)
    at Module._compile (module.js:456:26)
    at Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Module._load (module.js:312:12)
    at Module.require (module.js:364:17)

I tried to kick off that script with multiple users from my server console, and it worked all fine. As i said from my php-file it doesn't work.

Below is a snippet of my shell-script

export ANDROID_SDK=/srv/sdk/android-sdk
export MOBILE_SDK=/root/.titanium/mobilesdk
 
cd $WORKSPACE/sample_app
titanium build --sdk '3.4.1.GA' --build-only --platform 'android' --android-sdk $ANDROID_SDK > build.log 2>&1

May someone can help me, please. I look desperately for solutions... Thank you.