I've just uploaded KM 2.2.0. This rationalizes the parameters
controlling KM's behavior on error into a single variable, as
described below from the RELEASE-NOTES.txt:

2.2.0 - **NOTE**
        The parameters controlling behavior on errors have been
rationalized
        to a single parameter. *abort-on-error-report*, *error-report-
silent*,
        and *silently-abort-on-error-report* NO LONGER DO ANYTHING.

        Instead use the NEW variable *on-error* to define behavior on
errors,
        with the following allowed values:
           VALUE           KM'S BEHAVIOR ON ERRORS
           =====           =======================
           abort           Report error and do not continue, instead
                           immediately return NIL.
           abort-silently  Don't report error and do not continue, instead
                           immediately return NIL.
           debug           Report error and turn on debugger [DEFAULT]
           continue        Report error and continue.
           ignore          Don't report error and do continue.

        e.g., (setq *on-error* 'continue)

        NOTE that with continuation (*on-error* = continue or ignore),
KM will
        (as before when *error-report-silent* was t) assume a value of NIL
        for the computation where the error occurred. Again as before, this
        may cascade to cause other errors and may make the results of
        computation invalid, so use these two values with care.