One possible symptom of this issue is that a "switchshow" of the secondary switch will show "switchRole: Principal"
On the secondary switch (which you need to make sure is on a different domain ID) run these commands:
1. Portdisable (ISL ports)
5. Defzone –allaccess
6. Portenable (isl ports)
After this, the secondary switch should show as "switchRole: Subordinate"
This may also show up iniitally as a zoning conflict.