If it does not work when changing the permission this probably mean that the tmp and log path defined in the Global Configuration are not the one you think to be.
JMS used the path defined in Global Configuration.
Check the tmp and log path in the Global Configuration.
Your problem to use the Symbolic Link in JMS is not related to the hello.php file.
Add traces in "hello.php" will not help you as the code is different to the JMS one.
I repeat, the error in either in the path of tmp and log parameters present in the Global Configuration. They must be full path. In general this is a path that correspond to tmp and log directories present in the root of Joomla.
You have to check their permissions.
JMS use the standard tmp and log directories.
If you want that I check your environment, this is possible with billable support.
You can order such support on
www.jms2win.com/download?page=shop.produ...35&category_id=1