Hi Drusso,
I am sorry for the delayed response and for the trouble you had, please sign out from Acrobat once and reboot the machine and check for any pending updates of Acrobat from help>check for updates, reboot the machine after updating and try again.
What is the current dot version of Acrobat installed? To identify the version, refer to the steps mentioned in the article Identify the product and its version for Acrobat and Reader DC
For testing purpose, connect the machine to a different network environment like a guest wireless network or to a mobile hotspot or try sending the file for signature on your mobile device using cellular data and check.
Are you getting the error message with all the PDF files or with one specific PDF file?
Would you mind posting a screenshot of the error message you are getting? To post a screenshot, please refer to https://forums.adobe.com/docs/DOC-7043#jive_content_id_How_do_I_attach_a_screenshot
Let us know how it goes and share your observation.
Thanks,
Anand Sri.