mechanism array for exception frame frame-addr at mchvec-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 mechanism array for the exception frame at
    frame-addr is not accessible for reading. This vector lies at
    mchvec-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".