TU58 tape issues

So I decided to write a TU58 emulator for my 6809 SBC to serve "tapes" read side. It seems to work on an XXDP image I found online. However, when I try to boot an RT-11 tape image, I get: @1000G?BOOT-W-Error reading handler ?BOOT-W-Error reading handler ... ?BOOT-W-Error reading handler RT-11SJ V04.00A ?BOOT-W-Invalid or missing TT.SYS ?KMON-U-Overlay read error . .SHOW ?KMON-U-Overlay read error Any ideas on what might be causing this? I've dug up the old rtpip code and gotten it partially working in a more current environment, and it seems to be happy with the tape images I have. I've had this happen on two tape images. Also the original tapes from which these images were made are ones that I've booted from (after I made the tape images), albeit over 20 years ago. So it looks like either something strange in my tape images or something in my emulator that works to load the secondary boot, but fails for loading some other parts of the tape. BLS