Alex,
I'd be grateful if you could help. The PPA came as a life-saver to me. I had tried installing GNU-Radio, GRC, UHD, GQRX on 3 diff machines with fresh Ubuntu 13.04 on each; and these packages gave unique errors on all 3 machines! The PPA did wonders, to be honest. Now, I really don't want to downgrade to GR-3.6. For that, I'd have to remove all related packages, make sure there are no traces left whatsoever, and then check which versions of these half-a-dozen packages are compatible with each other, and then actually dig those old ones from their graves!
If there is a way, please help me.