Hello Jarry,
On Tue, 2011-01-18 at 21:10 +0100, Jarry wrote:
and after activating block I got white screen with some very nasty error message. It really scared me.
That'll teach you not to develop on live servers ;) . It helps if you read and try to understand the error message. Most likely the code you are loading contains errors which makes it unparsable and thus php bombs out and shows you an empty page. Use $ php -l <file> on a command line to check your php files for syntax errors.
While developing you can put ini_set('display_errors', 1); at the top of your php file. This will show all errors in the browser, so you don't have to keep the http error log open. Make sure to remove this statement when you transfer the file to the live site, because sometimes these errors contain sensitive information that you do not want to share with the rest of the world.
Setting error_reporting(E_ALL); also helps if the code that include your code set it to a lower level.
Regards, Leonard.