This appears when I attempt to boot up Polarisbloc:

XML error: Could not find parent node named "BaseGunSpecialAtlas" for node "ThingDef".

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This is the full log:

XML error: Could not find parent node named "BaseGunSpecialAtlas" for node "ThingDef". Full node: <ThingDef ParentName="BaseGunSpecialAtlas"><defName>MechRotaryCannon</defName><label>Rotary Cannon</label><description>Originally designed for being mounted on Imperial squad gunships, this 20mm rotary autocannon has been modified for use by the SM7 Battlemech. Takes an appreciable amount of time to spin up, but usually doesn't stop until the target is down. It's also capable of suppressive fire.</description><graphicData><texPath>Things/Item/Equipment/WeaponRanged/RotaryCannon</texPath><graphicClass>Graphic_Single</graphicClass><drawSize>3</drawSize></graphicData><statBases><MarketValue>1000</MarketValue><Mass>42</Mass><AccuracyTouch>0.15</AccuracyTouch><AccuracyShort>0.25</AccuracyShort><AccuracyMedium>0.5</AccuracyMedium><AccuracyLong>0.4</AccuracyLong><RangedWeapon_Cooldown>0</RangedWeapon_Cooldown></statBases><tradeability>None</tradeability><techLevel>Spacer</techLevel><destroyOnDrop>False</destroyOnDrop><menuHidden>False</menuHidden><weaponTags><li>MechM7Gun</li></weaponTags><verbs><li><verbClass>Verb_Shoot</verbClass><hasStandardCommand>true</hasStandardCommand><defaultProjectile>Bullet_RotaryCannon</defaultProjectile><range>30</range><warmupTime>3</warmupTime><ticksBetweenBurstShots>1</ticksBetweenBurstShots><burstShotCount>250</burstShotCount><soundCast>RotaryCannon</soundCast><soundCastTail>RotaryCannonSpin</soundCastTail><muzzleFlashScale>12</muzzleFlashScale><targetParams><canTargetLocations>true</canTargetLocations></targetParams></li></verbs><tools><li><label>barrel</label><capacities><li>Blunt</li></capacities><power>40</power><cooldownTime>2.1</cooldownTime></li><li><label>stock</label><capacities><li>Blunt</li></capacities><power>45</power><cooldownTime>2.2</cooldownTime></li><li><label>grip</label><capacities><li>Blunt</li></capacities><power>25</power><cooldownTime>2.5</cooldownTime></li></tools></ThingDef>
Verse.Log:Error(String, Boolean)
Verse.XmlInheritance:GetBestParentFor(XmlInheritanceNode, String)
Verse.XmlInheritance:ResolveParentsAndChildNodesLinks()
Verse.XmlInheritance:Resolve()
Verse.LoadedModManager:ParseAndProcessXML(XmlDocument, Dictionary`2)
Verse.LoadedModManager:LoadAllActiveMods()
Verse.PlayDataLoader:DoPlayLoad()
Verse.PlayDataLoader:LoadAllPlayData(Boolean)
Verse.<>c:<Start>b__6_1()
Verse.LongEventHandler:RunEventFromAnotherThread(Action)
Verse.<>c:<UpdateCurrentAsynchronousEvent>b__27_0()
System.Threading.ThreadHelper:ThreadStart_Context(Object)
System.Threading.ExecutionContext:RunInternal(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object, Boolean)
System.Threading.ExecutionContext:Run(ExecutionContext, ContextCallback, Object)
System.Threading.ThreadHelper:ThreadStart()

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Any ideas?