RCA RCU810 Won't Learn Certain Commands

I used to have one of those and it would learn practically any remote. I had
to replace it (fit of temper, threw it on the floor) with another one JUST
LIKE it. I find that this one won't learn anything at all from my Initial
DVD-2540 DVD player.

Now, that is a sort of "off-brand" DVD player and in fact they apparently
don't publish their remotes for code-entry, but that said my original sample
of the RCA RCU810 did successfully learn EVERY command from that remote.
This new one stubbornly refuses to do it.

It's not the batteries of the RCA or Initial; both were replaced. I also got
a replacement RCA remote and the 2nd sample also has this problem.

Tips?

LRH

Larry R Harrison Jr