Steel Bank Common Lisp

Hello,

I have big problems in a program and I can't understand what happens.
After hours, the program crashes and lands into the debugger. Once in the
debugger, I am trying to understand the problem but It looks like there
should have been big problems under the cover: I can't even inspect the
object, the debugger telling me the intrisic structure is invalid:

;;

0] frame 10
(RECEIVE #<MESSAGE {2528A9C9}>)
10] L
SB-DEBUG::ARG-0  =  #<MESSAGE {2528A9C9}>

10] (sb-debug:arg 0)

#<MESSAGE {2528A9C9}>
10] (slot-boundp (sb-debug:arg 0) 'src)


debugger invoked on a TYPE-ERROR in thread #<THREAD "initial thread"
{A6CC799}>:
  The value #<invalid object #x8A88FAD7> is not of type (SIMPLE-ARRAY T
(*)).

Type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.

;;

Note i am note using any exotic features such as multithreading but only
common lisp features
Any idea of what else to do ?

-Nicolas