After installing 8.5.1 Fix Pack 5 for Windows, Domino Designer will not function properly unless Notes is launched first.
Specifically, when you launch Domino Designer and then attempt to open an application from the Open Application dialog, a java.lang.UnsatisfiedLinkError will appear:
Additionally, attempts to create a new application could cause Domino Designer to hang.
This information is from TN 1450357
