This probably will not help you very much, but we've had _major_ problems running Silverstripe on PHP 5.1.2. Don't know about older versions. But from 5.1.6 on we've had no problems.

Try setting it to 64mb.

I've heard that the latest version requires more than 32mb. (This might be only when installing though.)

Alternatively try setting the memorylimit in your htaccess file:

php_value memory_limit 64M

Hello guys

Thanks for your great support! It works now!

Step by step we come to the point and by the way we detect some interesting facts

I've changed the saphire/main.php value from 32 to 64
ini_set("memory_limit","64M")

and also adapted the .htaccess from 32 to 64
php_value memory_limit 64M

Sitemap.xml
* * * * * * *
The sitemap.xml issue still persist. I've checked the page names and classes.
No doublets at all. But I have news!
I have figured out that when I changed the set_environment_type parameter in my _config.php from dev to live or remove it, the FATAL ERROR doesn't occure anymore.
Director::set_environment_type("live"); instead I have a new FATAL ERROR

Fatal error: Call to a member function getSession() on a non-object in .../sapphire/core/Session.php on line 32

God bless the session();

Mario