BiBiS wrote:
I'm trying edit skills.txt ...
what tool can edit patch_d2.mpq ...
I'm not familiar with any D2 Text File analyzer software, so do not know about the error messages you are seeing. I made my own python program to spell-check the files, and create some simple web pages based on their contents. One of the more effective modding strategies is to just make a small change and experiment with the effects in-game. It takes quite a long time, but there is not always accurate documentation for how to change the text-files, so you don't have many choices.
I use Ladik's MPQ editor to decompress an mpq file into it's files, and then edit the files using Open Office Calc (but MS Excel should work fine too). Make sure to configure your editor so that it understands that the text files are "tab-delimitated", and that when saving the file it should not store anything but text (no special spreadsheet functions, fonts, etc).
Consider reviewing
The Phrozen Keep for modding related questions.