Thanks nakashu for your solution to this problem.

I extended your solution to make it more flexible. instead of hardcoding the server path i used Director::baseFolder(). This way you can move your SS installation from a temp folder (e.g. mydomain.com/_testarea -> mydomain.com) without having to change the path manually in Backend.php.

Replace the code in sapphire/thirdparty/Zend/Cache/Backend.php in line 164 - 169 with this:

        } else {
            // unix...
            if (isset($_ENV['TMPDIR']))    return $_ENV['TMPDIR'];
            if (isset($_SERVER['TMPDIR'])) return $_SERVER['TMPDIR'];
            return Director::baseFolder().'/silverstripe-cache';
        }

my dear friend, it works now, I didnt understand the hole thing but just changed the code u write for us in the php file and it started to work...man all I have understand that it shold be changed if u put it onlne, In localhost, on ur pc need no change....Thanks to all, I'll be asking soon with every other things very soon...till then the problem for us is now solved...thanks again

Thanks to
nakashu
BigChris
silverseba

A webserver denied writing to the /tmp file with error code

[Warning] is_dir() [function.is-dir]: open_basedir restriction in effect. File(/tmp/) is not within the allowed path(s): (/webspace/12/49892/cc-institut.de:/webspace/12/49892/php_includes:/webspace/12/49892/php_sessions:/webspace/12/49892/temp)
GET /admin
Line 152 in /webspace/12/49892/cc-institut.de/sapphire/thirdparty/Zend/Cache/Backend/File.php

After reading through everything and looking at the code of all the mentioned sites, the post of silverseba finally got me fully enlightened ;)

Thank you all for posting your replies!

Kindest Regards,
Worp