The issue was not Android .

The issue was not Android. (Except perhaps the misleading error message.) The problem, it turns out, was that the pairings on the radio were "full". It seems this radio (CDE-133BT) allows 3 pairings. Well, I inadvertently renamed my Nexus some point along the way when I also unpaired it from the phone. Attempting to re-pair without first emptying a free slot on the radio failed. I do not know what the comms is like for denying a connection based on that, but either the radio sent incorrect information about why the pairing was denied or Android reported an incorrect reason. The problem is solved - By the way - the way to empty the bluetooth pairings is NOT in the manual - I watched a YouTube video of someone making pairings and discovered a way to find what the pairings were. Not sure if this Q/A still belongs here, but maybe it will be helpful for someone with an Alpine CDE-133BT someday.