Problem with Aggregate CSS files option and tmp directory
As per Drupal PHP requirements, safe mode should be off.

It will interfere with file uploads and possibly email sending as well.

You'll probably find you need, in all the .htaccess places with:

Options +FollowSymLinks 

to change to 

Options +SymLinksIfOwnerMatch

In any case, if you can't disable PHP "safe mode" which, according to php.net is deprecated 


  Safe Mode
  This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP
  5.4.0.


and the other options don't work - you may need to consider using another webhost.