Yes SatGuys covers the H21 rec. in the CE section.
http://www.satelliteguys.us/directv...61-h21-h23-ce-release-v-4339-7-17-7-18-a.html
Thats where you'll find update info normally unless it's one that D* pushed ....
I don't use the H21 so I don't know what the current National Release (NR) is.
Is this software you mentioned the NR or a CE (cutting Edge update) ...
If it's a CE update, YES you can go back to the NR, but if it's a D* sent one, no you can't.
From the issues you've mentioned, it sounds to me like your having issues on your end as well.
If you have the protection plan, have D* come out and check the rec'r ... if it's bad they will replace it. I'm thinking from what you said, it's a rcvr, not your TV, but haven't kept up on your issues either.