Error accessing namespace

Hum. Whenever an operation tries to access the namespace,
I get the following error:

Error while getting full update for HELL:
The first argument to the FAST-AREF-1 instruction, #\M, was not a string
character, and therefore will not fit in the ART-STRING array
"USER-PROPERTY ALL-ymbolics 0 \"Foo's desk\"PRANCE\"le\"....".

Where HELL is the name of my namespace, and the USER-PROPERTY is one
of a machine I recently added to said namespace.

What steps should I take to debug that?
(I have lost in a disk crash the meta-instructions I was sent
on this list about debugging LISP machines, which is also why
I asked about recent archives for this mailing-list.)

Happy new year!

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