I've seen that "Error accessing the WSUS Signing Certificate" as well. In my case, I've worked around it by launching the SCCM console as an elevated process (right-click the icon and select "Run as administrator") whenever I need to manage Ivanti Patch. There's probably a better way to fix this but I haven't gotten around to looking into it.
Thanks rgsteele, that is good advice and often the best workaround for this issue.
This is from the guide: “The user running Shavlik Patch must have Log on as a batch job rights and must be a member of the WSUS Administrators group on the WSUS server. In addition, if the WSUS Server is remote, the user must be a member of the local administrators group on the WSUS Server.”