[Sheet Metal Workbench] Error invalid thickness

[Oktober]

Hi all,

I have been using Freecad for a few years already but I am now playing with the sheet metal workbench and I can't seem to figure out why I keep getting an error message every time I want to unfold my parts. No matter what part I try to unfold or which face I select for the unfolding, I keep getting the same invalid thickness error message and then when I click OK I get the unfold failed error message as you can see in the screenshots below.
Has anyone any idea what is wrong here and how to fix it?
I also attach the two files I am working on right now in case that helps anyone to figure out what is going on here.

Screenshot_1.png (22.34 KiB) Viewed 676 times

Screenshot_2.png (23.91 KiB) Viewed 676 times

Screenshot_3.png (17.76 KiB) Viewed 676 times

Thanks a lot for your help

Here is my setup:
OS: Windows 10 Version 2004
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/United States (en_US)

[papyblaise]

Has anyone any idea what is wrong here and how to fix it?

yes, I can: the 2 edges are welded in the red circle, it is necessary to indent this area so that the edges are free

[Oktober]

OK, I have since learned how to do that and I still have the same problem.
File is attached.

Screenshot_5.png (18.11 KiB) Viewed 585 times

Thank you for your help, I really appreciate it.

[papyblaise]

the cutting of the corner "box2" is automatic with SheetMetal latest version, before "extend", provided that the 3 edges are cut at the same time
for unfold to work there must not be the slightest overlap, so the best solution, when we start is to add an unfold after each bend, if it does not work, we look for the cause, if it works, we erase it (unfold) and we continue, until we are a master of the profession

Edit
it is often enough to modify the R folding so that the edges do not overlap (from R = 1 to R = 0.1mm)
I tried on your file, if I modify the outer edges, it crashes due to the topological renaming, hence the need to test the unfold step by step rather than having a general crash the finished project