to fix the problem - do the following

 cd /sys/arch/pmax
 patch -p0 < clock.patch

rebuild and install a new kernel - then boot into singleuser - set
the date and time using the "date" command (date YYMMDDhhmm) and now
halt the machine using halt and boot into multiuser

Index: pmax/clock.c
===================================================================
RCS file: /cvs/src/sys/arch/pmax/pmax/clock.c,v
retrieving revision 1.5
retrieving revision 1.6
diff -u -r1.5 -r1.6
--- clock.c     1997/07/07 08:24:19     1.5
+++ clock.c     1998/01/19 10:45:39     1.6
@@ -326,7 +326,7 @@
 * and if it's outside that range, sets it to 1972-01-01.
 */
#if 1          /* testing, until we write time-of-year code as aboce */
-#define YR_OFFSET      24      /* good til dec 31, 1997 */
+#define YR_OFFSET      26      /* good til dec 31, 1999 */
#define DAY_OFFSET     /*1*/ 0
#else
#define YR_OFFSET      22