Problem Description:

The demo won't work if the 'CATALINA_HOME' environmental variable is set otherwise.
FIX:
add the following line somewhere in the beginning of the scripts (e.g. line 4):

(start-camunda.bat):
set CATALINA_HOME="%CD%\server\apache-tomcat-7.0.50"

(start-camunda.sh):
export CATALINA_HOME=$(pwd)/server/apache-tomcat-7.0.50