The value of the "p3_lkid" parameter contains a character that is not allowed or the value exceeds the maximum allowed length. Remove the character from the parameter value or reduce the value length and resubmit. If the error still persists, report it to our Customer Support team. Provide the URL of the page you were requesting as well as any other related information. 

Can someone add some info on why we get this error? What is required here to fix it?

I am using ProcessPdp paramaeters with Email delivery option. I get this error as soon as the document generation process is 100% and it moves to next page, which i guess is the email customization page, to enter To address, CC subject, email body etc.