I guess i found the problem. The error always occured when i used a outdated .dmop(145 and 282). So i changed the Package Version to 384(latest possible KDMO download) and it worked. I tried something more: I changed the KDMO Version to 282(vdmo) and then I started the launcher to update the game. The following error showed up:
283.zip 파일 접근 실패 : 알수 없는 에러 입니다 ( 에러번호 : 404)
283.zip file access failed: Unknown error has occured (error: 404)
The server couldn't find the zip files. Read the README(as I saw it, in dmopackman folder). I can't update the whole kdmo.dmop. Version 283 to 380 can't be patched, on those the error message pop up. 381 to 427 can be patched.