Denys contacted support:
I am experiencing the dreaded Error 3 in Replicator on Windows 8.1, and after reading Joe's post in the FAQ (https://helpdesk.karenware.com/kb/faq.php?id=21), I am wondering if my observations on the issue might be helpful in solving this, both for me and for other users with the same problem.
I just found the reason this happens. Thank you, Denys!
I'll document this well once tested by a few users who have been experiencing the problem.