Fatal Error with PDF Stamper AddOn

Hi Shaon,
i got a problem with the download when using the PDF Stamper. After purchase i try to download the PDF and klick “download”. Then i get this message: “Catchable fatal error: Object of class WP_Error could not be converted to string in /home/***/public_html/***/wp-content/plugins/wpdm-pdf-stamper/wpdm-pdf-stampers.php on line 204”

When i deactivate the PDF Stamper or swich it to “skip stamping this file” i can download the file as normal PDF without any stamp. So it looks like the PDF Stamper is causing the problem.

Maybe you could help me.

Thanks in advance!
Regards,
Matthias