We have not seen this particular error, we would need more information.
. Have you been able to merge any documents?
. Can you send the PRO2PDF template to support AT formidablepro2pdf DOT com?
. Can you limit the pdf to one field and try the export from the plugin’s EXPORT tab and let us know if it works?
If it works, send the PRO2PDF template that fails to support AT formidablepro2pdf DOT com.