Vinca link

I am running netware 4.11 on a netfinity 5500 with a backup server of the same spec running over a vinca link. does anyone know what triggers the switch over, cause it just switched without the primary server going down, broadcast message was (server name)has failed, backup server has taken over via vinca link (or something to that effect)

i went to www.vinca.com and couldn't find anything, but here is what comes to mind:

Do you have a dedicated link between the two servers for mirroring?
Is the cabling bad?
Are the NIC's failing?
Is one server abending?
Does the primary ever switch back?