Part of the process for creating a custom action for SharePoint Designer involves create a ".actions" file.
I’ve found and tried to use a sample template which starts off as:
<?xml version="1.0" encoding="utf-8" ?>
<Actions Sequential="then" Parallel="and">
However, that xmlns attribute prevents my environment from working. My actions don’t show up in SPD.
The solution is to strip out the xmlns attribute, do an iisreset and close/re-open SPD.