Question pdf export

I recently update the Kunena software to latest stable versioneas well the Joomla code to 1.5.18 but the export function in Kunena Forum fails as previously: a PDF file of 4KB is built up but the AcroReadear says:
Adobe Reader could not open 'file.pdf' because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded).
I think the question is in the 252 post of the thread I attempt to export because with smaller threads the bug is not revealed.
I checked out my server setting as well php.ini parameters but is all ok; the question remains where is the code problem in Kunena and how must modify the pdf generator function?
No one else encountered this problem?

Please anyone can try to test this link and eventually says me where is the bug in Kunena code or in php settings.
I need to export the thread in PDF before to close definitively and store the file for next purpose, but I obtain only a 4Kb PDF file that Acrobat won't open for the issue said in the previous message.

here the link to test:

www.elemirezolla.org/index.php?option=co...tid=12&id=13&lang=it

I installed the class.ezpdf script in the includes joomla directory and now a PDF will be genrated but the file is not correctly encoded and Acrobat cannot read it as well.
Anymore a suggestion from anyone?

Still the same error :

Try to increase the maximum execution time and memory limit in your php.ini.

Dear Friends
I solved the problem simply after kunena.forum.css modification (I commented 5 css lines) to make it compliant with CSS 2.1 level. No problem with memory size or time limit in the php.ini because I tested the website on my local Apache server too where I set the php.ini to all possible limits.
I suggest with any browser on Mac platform to make the CSS file 2.1 compatible and all works fine.

Hello,

Maybe you can explain what do you have changed, to help others users