This happened to me on my 1200T early this year. I think it's a compatibility problem with Commodore's CD filesystem and modern software/hardware. I don't know how to solve it, but it can be avoided by using a different CDFS.
If bookmark.device isn't in DEVS: adding it may help. I never checked that on my system, as I only had the Commodore filesystem mounted for CD32 emulation.
If you're not using Commodore's CDFilesystem, then I'm probably completely wrong here ;-)
