OK, now this is impossible (11/23+ and RL02-RLV12 problem)

I have this 11/23+ system with an RL02 drive and the RLV12 controller that won't boot XXDP. Attempting to boot XXDP v2.5 either halts at 000154 during the initial boot, or gives ?RD ERR messages from XXDP. The behavior is a little random - sometimes it halts at 154, sometimes you'll get a few ?RD ERRs and then it'll lock up, and sometimes you'll get far enough to get an actual prompt from the XXDP monitor, but even then you can't run anything. You just get more RD ERRs. OK, I know - bad drive or bad pack, right? Well, I've tried two different RL02 drives and two different XXDP packs with the same results. Better yet, I've connected one of those RL02 drives to another -11 (this time a 11/04 w/RL11) and that same drive with those same packs boots and runs with no complaints. The drive even passes all the ZRL??? diagnostics and ZRLM?? can scan the entire pack and finds no bad sectors. Better yet, I have another RL02 pack with RSX-11M v3.5 and that boots and runs on the 11/23 with the same RL02 and RLV12 with no apparent problems. Now that's really impossible - the same drive that won't boot XXDP will boot RSX? How can this be? It almost seems like it has to be a software problem with XXDP, but XXDP obviously works on a 11/23 and the RLV12/RL02. Is there some strange hardware compatibility or ECO issue with the RLV12 or the 11/23+? Is there something XXDP does with the drive that RSX doesn't? I'd run diagnostics on the RL subsystem, but I don't really have any other load path for XXDP on this system. I did pare the system down until there are only three cards in the backplane - CPU, memory and RLV12. No joy. And just on a whim I tried a different cable for the RL02 - still no joy. Thanks much, Bob Armstrong