خوب این طرف آب که کسی نتونست جواب مارو بده ولی جوابشو از جای دیگه پرسیدم .. اینجا مینویسم تا شاید به درد بقیه بخوره :

The solution I always use for the cache directory without prompt access on sites with shared hosting and no shell access:

* Install JoomlaXplorer.
* Create backup of files and database to be sure.
* Delete the cache directory with your FTP user (there's no irreplacable data in here).
* Create the cache directory with JoomlaXplorer, and change permissions to 755. Now the owner of the directory is the Apache user, which is the user Joomla runs under.