The signature plugin is working on all our sites as expected and there are no known issues. We are not familiar with a ‘serialize’ message or error. Are you able to provide a screenshot of the error?
Check the plugin’s SETTINGS tab that the “Enable local PDFTK” option is not checked. If not checked and the signature is not merging, we are happy to take a look at your installation if you complete this form. Otherwise provide us with more information and we’ll try to help you troubleshoot the issue you are having.
We remain at your service.