The code you have should be edited a bit. Since you are displaying Shaman and Paladin you will have to increment that number. You can't use 3 for both of them.
It should look something like the below (Note that I change the order to make abit more sense for raiding/grouping purposes. You can order them however you want, just make sure you edit the number part of the name of your PRHeader frames.)
Code:
self:CreateRaidFrame("PRHeader1", "Warrior", "WARRIOR", nil, PRHeader1)
self:CreateRaidFrame("PRHeader2", "Priest", "PRIEST", nil, PRHeader1)
self:CreateRaidFrame("PRHeader3", "Druid", "DRUID", nil, PRHeader1)
self:CreateRaidFrame("PRHeader4", "Pally", "PALADIN", nil, PRHeader1)
self:CreateRaidFrame("PRHeader5", "Shaman", "SHAMAN", nil, PRHeader1)
self:CreateRaidFrame("PRHeader6", "Rogue", "ROGUE", nil, PRHeader1)
self:CreateRaidFrame("PRHeader7", "Mage", "MAGE", nil, PRHeader1)
self:CreateRaidFrame("PRHeader8", "Warlock", "WARLOCK", nil, PRHeader1)
self:CreateRaidFrame("PRHeader9", "Hunter", "HUNTER", nil, PRHeader1)