What steps will reproduce the problem?
1. First event of the 5-man instance "Trial of the Champion"
2. When players of my group are mounted on their "Argent Warhorse"
3. Error is spammed every 2 or 3 seconds

What version of the product are you using?
3.0.5

Do you have an error log of what happened?

Message: Interface\AddOns\XPerl\XPerl.lua:2401 attempt to index field 'conf' (a nil value)
Time: Fri Aug  7 19:29:54 2009
Count: 301
Stack: [string "Interface\FrameXML\BasicControls.xml:<Scrip..."]:18: in function <[string "Interface\FrameXML\BasicControls.xml:<Scrip..."]:4>
(tail call): ?
[C]: ?
Interface\AddOns\XPerl\XPerl.lua:2401 in function `XPerl_GetBuffButton'
Interface\AddOns\XPerl\XPerl.lua:2737 in function `XPerl_Unit_UpdateBuffs'
Interface\AddOns\XPerl_PartyPet\XPerl_Party_Pet.lua:288 in function `XPerl_Party_Pet_Buff_UpdateAll'
Interface\AddOns\XPerl_PartyPet\XPerl_Party_Pet.lua:447 in function `func'
Interface\AddOns\XPerl_PartyPet\XPerl_Party_Pet.lua:384 in function <Interface\AddOns\XPerl_PartyPet\XPerl_Party_Pet.lua:378

Locals: