[TYPO3-english] Fatal error with module-type extension when upgrading from TYPO3 4.2.9 to 4.4.2

[Jochem Nabuurs]

Hi list,

I'm having difficulties with updating a TYPO3 installation from 4.2.9 to 
4.4.2

I've created an extension which is a backend module. With it, users can
upload certain files. After the update, when I select the module, I get 
the following error:

Fatal error: Cannot redeclare xdebug() (previously declared in 
/var/www/sites/.../html/typo3_src-4.4.2/t3lib/config_default.php:489) in 
/var/www/sites/.../html/typo3_src-4.4.2/t3lib/config_default.php on line 493

The function xdebug exists only once in the file, on line 489.
I think the error occurs because the file is included twice (somewhere) 
but if that's so, then why are the linenumbers different??

Maybe it's a dumb question, maybe it isn't.
Anyway, I hope someone can provide me with some hints because I'm stuck.

Thanks in advance!

Jochem