Impossible to load the image - PHP generated images - Page 1

Hi all,

I'm trying to embed graphs created using pChart (http://pchart.sourceforge.net). This generates graphs as PNGs. The files look fine, and can be opened in a browser. The image URLs contain query strings, like:

chart_ss.php?a1=75&a2=85&a3=98&y=2011

When I try this with HTML2PDF, I get an error:

ERROR n°6
File : /home/sites/public_html/inc/html2pdf/html2pdf.class.php
Line : 1319

Impossible to load the image http://mydomain/chart_ss.php?a1=75&a2=85&a3=98&y=2011

Any ideas on why this happens and how to fix it?

Thanks!