i'm getting a "masterfile: potentially duplicate navmesh map" error when opening my mod.
what do i do about this?

i've tried deleting the navmesh map the error points to in tesSnip, this gave me a ~"navmesh map has no parent space, ignoring"-message on opening in creation kit, and ck would freeze forever when switching into navmesh mode in one of those cells, so this one's definitely a no can do.

happy about any hint, thx

First: Don't use TESVSnip. It corrupts data and you'll only do further damage by using it.

Second: The navmesh map is a different record. You'll need to use the CK's Details screen to remove the NAVI record. Make a backup first, because sometimes removing that will cause the CK to CTD while the mod is loading.

Third: The navmesh has no parent error is present for everyone. It's a defect in Skyrim.esm that hasn't been corrected.

oh.
now that's bad, thought i could use that just like fnvedit (been out for a while) - what does it corrupt, and/or is there anything else you can use for cleaning your mod? (except ck, i find it a big pain do to it there)

ah yes, it worked this way, thanks a lot.

ah, thx, came to ignoring those up to a level close to complete unawareness...
well then, so i know a workaround for this one now: get yourself a duplicate navmesh map, you won't get the parent space error anymore then

I had this same issue in my mod, along with unexplained in game CTD in a neighboring cell.
I had modded one cell, the neighboring cell had a repeatable CTD, and another cell over, the duplicate mesh showed up.
I have no idea what causes this.
However, I am obviously not the only one to experience this.
I think the duplicate Navmesh issue needs to be elevated to bug status.

It may well need to be, but it's so sporadic as to be unreproducable. The one time I had it happen I was not able to make it happen again. The only common thing is that it seems to show up after finalizing a cell.

In OP's case it was the NAVI record that duplicated, which has been an even less common occurrence that goes all the way back to Fallout 3 mods.

@s7o: TESVSnip will corrupt cell data as well as NPC data. Regardless of what you're using it for, once it goes to save your mod, you're pretty well done. There's quite a few other things that it only sometimes corrupts, but sometimes getting cancer is still bad, so it should be avoided entirely. The CK Details screen is currently the only safe option that exists for mod cleanup. Other utilities don't have the editing capabilities yet.

in my case, the error disappeared after deleting the navi-record, but since then, it tells me of all my ext cell their navmeshes need to be refinalized, no matter how often i do so

yeah right, this'd at least explain how all my npc's suddenly were named "lookup failed"

ok thx for info. wicked thing though, since i was just getting to pt2 in my 1-build-and-don't-give-a-****-2-clean-up-mess-afterwards - workflow...