Same error. The only other mods I have are Harmony and Hugs.

RimWorld 1.1.2564 rev670
Verse.Log:Message(String, Boolean)
RimWorld.VersionControl:LogVersionNumber()
Verse.Root:CheckGlobalInit()
Verse.Root:Start()
Verse.Root_Entry:Start()

[HugsLib] version 7.1.0
Verse.Log:Message(String, Boolean)
HugsLib.Utils.ModLogger:Message(String, Object[])
HugsLib.HugsLibController:InitializeController()
HugsLib.HugsLibController:EarlyInitialize()
HugsLib.Core.HugsLibMod:.ctor(ModContentPack)
System.Reflection.MonoCMethod:InternalInvoke(Object, Object[], Exception&)
System.Reflection.MonoCMethod:InternalInvoke(Object, Object[])
System.Reflection.MonoCMethod:DoInvoke(Object, BindingFlags, Binder, Object[], CultureInfo)
System.Reflection.MonoCMethod:Invoke(BindingFlags, Binder, Object[], CultureInfo)
System.RuntimeType:CreateInstanceImpl(BindingFlags, Binder, Object[], CultureInfo, Object[], StackCrawlMark&)
System.Activator:CreateInstance(Type, BindingFlags, Binder, Object[], CultureInfo, Object[])
System.Activator:CreateInstance(Type, Object[])
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()

Exception filling window for RimWorld.Page_ConfigureStartingPawns: EdB.PrepareCarefully.InitializationException: Prepare Carefully failed to initialize ---> System.MissingMethodException: void Verse.PawnGenerationRequest..ctor(Verse.PawnKindDef,RimWorld.Faction,RimWorld.PawnGenerationContext,int,bool,bool,bool,bool,bool,bool,single,bool,bool,bool,bool,bool,bool,bool,bool,single,Verse.Pawn,single,System.Predicate`1<Verse.Pawn>,System.Predicate`1<Verse.Pawn>,System.Collections.Generic.IEnumerable`1<RimWorld.TraitDef>,System.Collections.Generic.IEnumerable`1<RimWorld.TraitDef>,System.Nullable`1<single>,System.Nullable`1<single>,System.Nullable`1<single>,System.Nullable`1<Verse.Gender>,System.Nullable`1<single>,string,string,RimWorld.RoyalTitleDef)
at EdB.PrepareCarefully.PawnGenerationRequestWrapper.get_Request () [0x00000] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.Randomizer.GenerateColonist () [0x00006] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.RelationshipManager.ComputeInverseRelationship (RimWorld.PawnRelationDef def) [0x00000] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.RelationshipManager.PopulateInverseRelationships () [0x0003b] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.RelationshipManager..ctor (System.Collections.Generic.List`1[T] originalPawns, System.Collections.Generic.List`1[T] correspondingCustomPawns) [0x00084] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.PrepareCarefully.InitializeRelationshipManager (System.Collections.Generic.List`1[T] pawns) [0x00051] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.PrepareCarefully.Initialize () [0x0001c] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at EdB.PrepareCarefully.HarmonyPatches.PrepareCarefullyButtonPatch.Postfix (RimWorld.Page_ConfigureStartingPawns __instance, UnityEngine.Rect& rect) [0x0008c] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
--- End of inner exception stack trace ---
at EdB.PrepareCarefully.HarmonyPatches.PrepareCarefullyButtonPatch.Postfix (RimWorld.Page_ConfigureStartingPawns __instance, UnityEngine.Rect& rect) [0x000fc] in <93cfe9e5785042fcab5eb0a8cc28d14a>:0
at (wrapper dynamic-method) RimWorld.Page_ConfigureStartingPawns.DMD<DMD<DoWindowContents_Patch1>?-1363507456::DoWindowContents_Patch1>(RimWorld.Page_ConfigureStartingPawns,UnityEngine.Rect)
at Verse.Window.InnerWindowOnGUI (System.Int32 x) [0x00165] in <56c3d53315e64465a345345159dd2fd3>:0
Verse.Log:Error(String, Boolean)
Verse.Window:InnerWindowOnGUI(Int32)
UnityEngine.GUI:CallWindowDelegate(WindowFunction, Int32, Int32, GUISkin, Int32, Single, Single, GUIStyle)

I tried dragging EdB to the top of my mod load order and it seems to have worked.

im having this exact problem righht now a year later and the mod for me is already at the top, im not sure why prepare carefully causes this

Originally posted by Arizona Ranger:

im having this exact problem righht now a year later and the mod for me is already at the top, im not sure why prepare carefully causes this

Which version of RimWorld are you running? The original post says that they are running RimWorld version 1.1.2564. That's a pretty old version of the game, and I honestly haven't tested against that version in a long time. You might try to manually install an older version of the mod: https://github.com/edbmods/EdBPrepareCarefully/releases/tag/v1.1.9

It sounds like I may need to update the mod to page to show that 1.1 is not supported anymore.