I tried several times to start fresh, deleting everything and all drivers relating to the HL2270, and then installing the 2012 drivers downloaded from Brother. That did not work - still got the invalid driver message. After reading the posts in this thread,
I then deleted the PostSPUpgrade key, and started fresh again with a new driver installation, but that still did not resolve the printing issue and the "invalid driver" box.
I finally did get the printer to start working again by starting fresh one more time. I downloaded the uninstall tool from the Brother website and uninstalled the printer and driver, so that there were no references anywhere to the Brother printer, or if
there were I deleted those (after running the uninstall tool from Brother, I was able to get around Windows refusal to delete the Brother driver package because it spuriously claimed the driver was in use).
Now, with the Brother HL2270 driver and hardware completely removed in all respects, I pulled out the original installation CD that came with the printer, disconnected the 2270 and hooked up a portable CD drive to the computer, and then followed the installation
instructions, just as if the printer were newly acquired and being installed for the first time. After that installation, the printer worked again. I have not tried to update the driver, because of fear that it will again become nonfunctional, but at least
it appears to be printing without problem now. The deletion of the PostSPUpgrade key, before the printer and driver re-installation from the CD, may have helped here, but I don't know for sure.