There is NOTHING in the PDF packingslip file that should cause the error you are describing...
UNLESS
You are not running PHP 5..

Doh!!! I was tired and busy as heck on Saturday when you first posted.. Don't know why I didn't PAY ATTENTION..

I sorta just generally assumed that mosts hosts no longer supported PHP 4.. My bad..
In the testing environments of ALL of the beta testers and developers of this mod we were all running SQL 5.2 or better and PHP 5.2.x or better.
This mod was specifically tested to make sure that it was not only PHP 5.3 compatible, but backwards compatible for those hosts still running PHP 5.2.x. If your hosting environment is running a version of PHP lower than 5.2.x than THAT would be the reason you are getting this error.
Your server is probably currently running version 4.x of php. Do you have the ability to upgrade? Who is your hosting through? Most of the major hosting providers (Godaddy, ipower, gator, etc) have some form of 5 running. Sometimes you can switch between version 4 and 5.
Bookmarks