I very often get this error on my Feral Druid and my Enhancement Shaman:
Version 7.0.18.0:

Message: Interface\AddOns\Ovale\Cooldown.lua:215: attempt to perform arithmetic on local 'cdStart' (a nil value)
Time: 09/24/16 21:26:45
Count: 436
Stack: Interface\AddOns\Ovale\Cooldown.lua:215: in function GetSpellCooldown' Interface\AddOns\Ovale\Cooldown.lua:433: in functionGetCD'
Interface\AddOns\Ovale\Cooldown.lua:325: in function ApplyCooldown' Interface\AddOns\Ovale\Cooldown.lua:316: in function?'
Interface\AddOns\Ovale\State.lua:82: in function InvokeMethod' Interface\AddOns\Ovale\Future.lua:1428: in functionApplySpell'
Interface\AddOns\Ovale\Frame.lua:309: in function UpdateActionIcon' Interface\AddOns\Ovale\Frame.lua:221: in functionOnUpdate'
Interface\AddOns\Ovale\Frame.lua:89: in function <Interface\AddOns\Ovale\Frame.lua:88>

Locals: self =

{
gcd = {
}
SetDefaultModuleLibraries = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:398
Enable = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:325
UnregisterAllEvents = defined @interface\AddOns\Bagnon\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:202
GetGlobalCooldown = defined @interface\AddOns\Ovale\Cooldown.lua:164
EnableModule = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:363
modules = {
}
GetModule = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:241
IterateEmbeds = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:473
StartProfiling = defined @interface\AddOns\Ovale\Profiler.lua:124
defaultModuleLibraries = {
}
baseName = "Ovale"
SaveSpellcastInfo = defined @interface\AddOns\Ovale\Cooldown.lua:238
GetSpellCooldown = defined @interface\AddOns\Ovale\Cooldown.lua:178
SetDefaultModulePrototype = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:440
ApplySpellStartCast = defined @interface\AddOns\Ovale\Cooldown.lua:302
CleanState = defined @interface\AddOns\Ovale\Cooldown.lua:292
InitializeState = defined @interface\AddOns\Ovale\Cooldown.lua:287
name = "Ovale_OvaleCooldown"
RequireCooldownHandler = defined @interface\AddOns\Ovale\Cooldown.lua:249
IsEnabled = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:482
orderedModules = {
}
StopProfiling = defined @interface\AddOns\Ovale\Profiler.lua:124
DisableModule = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:381
statePrototype = {
}
CopySpellcastInfo = defined @interface\AddOns\Ovale\Cooldown.lua:231
GetBaseGCD = defined @interface\AddOns\Ovale\Cooldown.lua:219
ApplySpellAfterCast = defined @interface\AddOns\Ovale\Cooldown.lua:312
RegisterMessage = defined @interface\AddOns\Bagnon\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:118
UnregisterMessage = defined @interface\AddOns\Bagnon\libs\CallbackHandler-1.0\CallbackHandler-1.0.lua:181
Update = defined @interface\AddOns\Ovale\Cooldown.lua:136
OnEnable = defined @interface\AddOns\Ovale\Cooldown.lua:84
IsSharedCooldown = defined @interface\AddOns\Ovale\Cooldown.lua:154
defaultModuleState = true
DebugTimestamp = defined @interface\AddOns\Ovale\Debug.lua:180
IsModule = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:248
OnDisable = defined @interface\AddOns\Ovale\Cooldown.lua:101
SetDefaultModuleState = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:418
AddSharedCooldown = defined @interface\AddOns\Ovale\Cooldown.lua:159
OnInitialize = defined @interface\AddOns\Ovale\Cooldown.lua:73
SetEnabledState = defined @interface\AddOns\Dominos\libs\AceAddon-3.0\AceAddon-3.0.lua:455