Help needed with PDP-11/35 and XXDP problem

Hello readers. I have two questions which are in a sense related. I have a problem with my PDP-11/35 and withn XXDP+. When I boot my 11/35 it reports RT11-SJ (S) V04.00E. This version runs perfectly. When I try to boot RT11-FB V5.4 the VIRTUAL LED on the console goes on and at that moment the system hangs. I did check all the required jumper changes on the other CPU boards but the memory management unit M7238 was already installed in the system and the jumpers all seem to be correctly set. Anyway, when I boot that RT11-FB version on my PDP-11/34 it runs just fine. Needless to say that both are _real_ machines. When that RT11 version is booted on the 11/35 the ADDRESS LEDs show 076602 and the DATA LEDs show 177620. The MMU occupies address range 777600-777676. Is this a coincidence ? Last week I got the RL02 drives connected to the 11/35. I have a pack with XXDP+ on it and I hoped to run the diagnostics for the CPU and the MMU. When I have XXDP+ booted (that goes well) and enter the command "R BKTGD1.BIC" the READY light and on the 11/35 the ADDR and DATA LEDs blink a few seconds but then the system hangs. ADDR LEDs show 001156, DATA shows 000767. On the console terminal is the text "KT11-D EXERCISER DBKTG-D". Does anybody have any clues on how to proceed? How do I use XXDP, any manual anywhere ? TIA, Henk Gooijen gooi(a)oce.nl