The most common failure while the Creation Kit is building Precombines is "Access violation 0xc000005" (or similar) which is normally due to a corrupt/incompatible Mesh on a Precombineable Reference (i.e. a REFR with base type STAT or SCOL). Below is my guide to finding and resolving these.

If Creation Kit does not start at all then your problem is not in a mod but your PC setup. See the Stick Post on setting up your PC environment - particularly when using Steam version of CK - as you MUST set up the Steam_AppId.txt correctly AND (if using MO2) set up FO4Edit.exe and GeneratePrevisbines.bat as "Executables" with the correct AppID override.

1) Find the Cell that contains the problem References:

You need the log from the Creation kit for this. It will normally be something like CK.log (located in the same directory as Creationkit.exe). If you cannot find it then you probably did not specify a log in the CreationKitPlatformExtended.ini settings file as recommended by me. Do it and repeat.
Look for the last "DEFAULT: Generating for ..." line. Interior cells will just give you the EditorID for that cell, Exterior Cells will give you the Cell ID.

2) Check for problem meshes in the Mods that touch this cell:

Open up xEdit/FO4Edit with JUST your Patch Mod selected, and go to this Cell. Now look at the Mods that touch this cell (in the right hand pane) and note them down (you can ignore Base Game, DLCs, UFO4P and PRP/PPF). These are our first suspects.
While in xEdit, highlight/select ONLY these mods (You can select individual mods by pressing CTRL while clicking on them), right click and select "Apply script...", choose FO4FindNewPCStatics.pas, and ok. This script will scan all those plugins for new Meshes that will crash the CK and list them with an ! in front of their names.
If it finds some then click "Exclude bad" and it will update your Patch to exclude them. Hope fully you have found the problem! Try re-running the Precombine Phase again.
If nothing found (or it still crashes at the same cell) then it could be a Mesh replacer mod (as these don't add Cell overrides).

3) Finding problems due to  Object replacement Mods:

The problem could be a Mod that just replaces Objects themselves - such as a 'HD models' type mod. Finding bad meshes from these mods will be easier if you don't use mods with loose files (i.e. all mods have <modname> - Main.BA2 files). In this case load up xEdit but ONLY wuith your patch mod, select ALL the mods (except your Patch Mod), right-click and "Apply Script...", choose FO4FindNewPCStatics.pas, and ok. This may take a long time. Again look for meshes with !, exclude them, and retry your precombine phase.

If, however, your setup includes mod with loose files (or you don't know) then your only option is to load your entire load order into xEdit and run the above script against everything (except your patch mod). This will take a long time. If nothing is found then perhaps the issue is a Texture replacer.

4) Finding problems due to Texture Replacer Mods:

Corrupt Textures can crash the CK too. These mods usually perport to 'use less video RAM' or are 'HD' replacements to common objects. It is difficult to narrow down which one is causing the issue with the particular Cell that crashes (unless you know it contains objects effected by a Texture replacer) so I would treat ALL texture replacers as suspect.
Texture replacer mods will contain <modname> - Textures.BA2 archive, or loose ".dds" files.
If you only use Texture replacers without loose files, then you only need to concentrate on ones that are listed as a "Master" of your Patch Mod (when in xEdit, click on the "File Header" and the "Masters" will be listed in the Right hand pane).
If you have Mods with loose Textures then all of those are suspect.

To isolate whether it is a Texture replacer at fault, temporarily disable ALL suspicious Texture replacers (you found above), Recreate your Patch and retry generating Precombines.
If it no longer crashes then you may want to selectively re-enable each Texture Mod until it again crashes (to isolate the problem mod).

Note: If a Mod ONLY contains Texture replacements then you do not need to have it enabled when you are generating a Previsbine Patch. Your new Previsbines will display whatever Textures are available when the game is running - so they do not need to be there when generating Precombines.

Generating Precombines for a single Cell:

This can be useful during this fault finding process as running a complete Precombine build to see if you found the problem could be time consuming.
Instead what you can do is generate a 'single cell previsbine patch' just for test purposes and use GeneratePrevisbines.bat against that.

To do this load up your complete Load order in xEdit, then find the Cell that you want to test against (either search for its FormID if exterior, or EditorID if Interior).
Now right-click on it, select "Apply script...", choose FO4Check_Previsbines.pas, on it's options click "Create Seed to rebuild Previs .. to improve FPS" (or whatever option you originaly used to create your Patch) AND "Process ONLY plugins you highlighted" and click OK. This will create an xPrevisPatch.esp you can use to just test building that one Cell that failed.

How to Manually Exclude a Reference from being Precombined:

Both FO4Check_Previsbines.pas and FO4FindNewPCStatics.pas do this automatically, but if you want to edit a mod to deliberately stop a REFR from being precombined (because it crashes the CK or you want to be able to select it in-game) then you can either exclude a specific REFR by setting it's "XLRT - Location Ref Type" to NoObjectCombinationRefType, or find it's base object (NAME - Base) and exclude that by setting its "FTYP - Force Loc Ref Type" to NoObjectCombinationRefType. Note that this stop all references that use that base object from being precombined (useful if this Base object uses a bad mesh).

Created: PJM Mar 2025