Just as additional information:
There is a php.ini directive called
disable_functions. Functions added to this list will be disabled by PHP and when you try to execute those functions, you get this error. As mentioned, in all probability your hosting provider has added
exec to the disabled list. This is a common practice in shared hosting. You will need a dedicated server if you really want to run
exec (or some hosting provider who provides
It is a bad idea to trust a shared hosting provider who allows you to run exec unrestrained.
Those errors mean just what they say.
Fatal error: Call to undefined function execute()
You are calling a function that doesn't exist.
Warning: exec() has been disabled for security reasons
Your web host has disabled the
exec() method, you won't be able to run background scripts (like it appears you are attempting to do). You'll need to find another way to accomplish your goal, or find another web host.