Everything was working fine until today's RimWorld update. I used the properties menu to revert to 1.1.262, made sure my mods are loading in the correct order, and now I'm getting:

Error while instantiating a mod of type Rimefeller.RimefellerMod: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> HarmonyLib.HarmonyException: Patching exception in method null ---> System.ArgumentException: Undefined target method for patch method static System.Void Rimefeller.H_IsFloorAllowed::Postfix(Verse.TerrainDef floor, System.Boolean& __result)
at HarmonyLib.PatchClassProcessor.PatchWithAttributes (System.Reflection.MethodBase& lastOriginal) [0x0004d] in <20181e2d55204880a56a9120ef04a53d>:0
at HarmonyLib.PatchClassProcessor.Patch () [0x00057] in <20181e2d55204880a56a9120ef04a53d>:0
--- End of inner exception stack trace ---
at HarmonyLib.PatchClassProcessor.ReportException (System.Exception exception, System.Reflection.MethodBase original) [0x00127] in <20181e2d55204880a56a9120ef04a53d>:0
at HarmonyLib.PatchClassProcessor.Patch () [0x00082] in <20181e2d55204880a56a9120ef04a53d>:0
at HarmonyLib.Harmony.<PatchAll>b__10_0 (System.Type type) [0x00007] in <20181e2d55204880a56a9120ef04a53d>:0
at HarmonyLib.CollectionExtensions.Do[T] (System.Collections.Generic.IEnumerable`1[T] sequence, System.Action`1[T] action) [0x00014] in <20181e2d55204880a56a9120ef04a53d>:0
at HarmonyLib.Harmony.PatchAll (System.Reflection.Assembly assembly) [0x00006] in <20181e2d55204880a56a9120ef04a53d>:0
at Rimefeller.RimefellerMod..ctor (Verse.ModContentPack content) [0x00018] in <06aca2482fb2462b88b462df73494cc6>:0
at (wrapper managed-to-native) System.Reflection.MonoCMethod.InternalInvoke(System.Reflection.MonoCMethod,object,object[],System.Exception&)
at System.Reflection.MonoCMethod.InternalInvoke (System.Object obj, System.Object[] parameters) [0x00002] in <567df3e0919241ba98db88bec4c6696f>:0
--- End of inner exception stack trace ---
at System.Reflection.MonoCMethod.InternalInvoke (System.Object obj, System.Object[] parameters) [0x00014] in <567df3e0919241ba98db88bec4c6696f>:0
at System.Reflection.MonoCMethod.DoInvoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0007a] in <567df3e0919241ba98db88bec4c6696f>:0
at System.Reflection.MonoCMethod.Invoke (System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <567df3e0919241ba98db88bec4c6696f>:0
at System.RuntimeType.CreateInstanceImpl (System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes, System.Threading.StackCrawlMark& stackMark) [0x00213] in <567df3e0919241ba98db88bec4c6696f>:0
at System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes) [0x00095] in <567df3e0919241ba98db88bec4c6696f>:0
at System.Activator.CreateInstance (System.Type type, System.Object[] args) [0x00000] in <567df3e0919241ba98db88bec4c6696f>:0
at Verse.LoadedModManager.CreateModClasses () [0x00076] in <4489f1367c1c4d76b2ae1272c8ed691d>:0
Verse.Log:Error(String, Boolean)
Verse.LoadedModManager:CreateModClasses()
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()

Any ideas? Again, this was working fine yesterday.