signal vector for exception frame frame-addr at sigvec-addr is not
 readable

    Facility: DEBUG, VMS Debugger

    Explanation: The debugger is attempting to chain down the call
    stack, following frame pointers. The debugger has determined
    that part or all of the signal vector for the exception frame
    at frame-addr is not accessible for reading. This vector lies
    at sigvec-addr. This usually indicates a corrupt frame list, but
    could also indicate that the program has protected part of memory
    in which the frame lies. In either case, this is an error.

    User Action: Determine what part of your code is writing into the
    FP register or overwriting the saved frame pointer on the call
    stack (or a preceding saved frame pointer) and correct it. Since
    the debugger looks at the call stack to symbolize addresses, you
    may suppress some of these messages by typing the command "SET
    MODE NOSYMBOLIC".