[BlueOnyx:01426] PHP writing files - where can I do it

[Support]

Hello,

I am trying to use PHP to write a file (fopen(... ,'w') on BO but for some
reason even if I manually change the permissions on a file that exists the
php code (from php.net as a fallback test) cannot open the file.

I have tried lot's of different things but nothing seems to work as
expected.

Is there a specific way that I should be doing this?

Tony