I recommend following the exact format that the developers used.
for example
Codedata/scenarios/mp/4p_Uneventest01/4p_Uneventest01.sgb
Also, just to rule out, have you verified game cache integrity, of Companyofheroes2 in steam? I doubt this is your problem, but it never hurts to check.
Verified game cache
Renamed file, placed it in Mp subfolder
Error messagde is now:
Archiver failed!
Command line:
"C:\Program Files (x86)\Steam\steamapps\common\company of heroes 2\archive.exe" -c "C:\Users\Användaren\Documents\My Games\Company of Heroes 2\PackageBuildFile.txt" -a
"C:\Users\Användaren\Documents\My Games\Company of Heroes 2\mods\scenarios\4p_notworkingtest01.sga" -r
c:\program files (x86)\steam\steamapps\common\company of heroes 2\coh2\data"
Looking at it now, it doesn't include the "mp" or the subfolder in the string above, is it supposed to be like that?