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