The cache is not working on Debian 6... fastcgi module in apache2. How can I make shared memory accessible ?

System Linux myhost 2.6.32-5-amd64 #1 SMP Mon Mar 7 21:35:22 UTC 2011 x86_64
PHP version 5.3.6-6~dotdeb.1
PhpExpress version 3.0.1 (build 3025)
Debug build no
Thread safety disabled
Server API CGI/FastCGI
Server software Apache/2.2.16 (Debian)
Configuration none, none, none
Memory types local, mmap_posix, mmap_anon, sysvipc, mmap_zero, mmap_file
Semaphore types posix, fcntl, spinlock, pthread, sysvipc, flock
Shared memory ID
Cache owner -1
Shared memory accessible no
Status mem error=0, semaphore error=0, status=1

please run ab -c 15 -n 45 http://yourwebsite then check parent process ID (pid) for all php child processes.
Let me know what you see.
and it's better to submit a ticket using http://www.nusphere.com/contact_us