I have HSO dated 2011. It seems to be working fine.
When I search for *.fxp I get NOTHING.
When I search for *.fxb I get NOTHING.
I must have a different version? I think 1.5 was the latest, and that was 2009. The 2011 copyright I see must be due to some sort of update, 64-bit version, VST 3 version or something. You probably have the same version and updates. But maybe not.
What I don’t have is Dorico beyond the free version. So maybe it’s Dorico-related. Maybe one has to be installed before the other. I’d ask for support from Steinberg if you still have this issue.