Are you truly talking about a second cluster, or do you mean the second member of the cluster?
I have two SA4000 FIPS units in a cluster in an active/passive config. They normally both show green in the Status page.
I have noted that after every upgrade (6.4r2 this morning) the second unit goes red. Even though I am installing on the cluster virtual IP it doesn't concurrently install on the second member -- only on the primary member.
It also never does a resync. I previously tried overnight, just to see what it would do. Nothing.
I have found that I need to power down the second member. I leave it off about 10 seconds, then power up. After about 15 minutes it will go green in the Status page.