[TYPO3-english] introductionpackage won't start, server problem?

[bernd wilke]

hi, I got a problem with the introductionpackage (4.4.3) but I think 
probably it is a server problem 

I installed the introductionpackage (=IP) and selected a bright color.

trying to change the color afterwards to a darker tone all got broken.

I renamed the dir of this installation and created a new dir with the old 
name. Then I did a second new unzip, which seems broken from the 
beginning:
starting the install-tool (either mode) results in errors like: 
Fatal error: Class 't3lib_DB' not found in /var/www/intro/t3lib/
class.t3lib_div.php on line 5248 

are there any (php-include-)caches of server which could cause this error?
how to remove/ clear it?

server-configuration:

Linux buro 2.6.32-25-generic #44-Ubuntu SMP Fri Sep 17 20:05:27 UTC 2010 
x86_64 GNU/Linux 

Apache/2.2.14 (Ubuntu) 

Suhosin Patch 0.9.7
Zend Engine v2.2.0, Copyright (c) 1998-2009 Zend Technologies
    with XCache v1.2.2, Copyright (c) 2005-2007, by mOo
    with Xdebug v2.0.4, Copyright (c) 2002-2008, by Derick Rethans
    with Suhosin v0.9.28, Copyright (c) 2007, by SektionEins GmbH

PHP_VERSION  : 5.2.10-2ubuntu6.4

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