It's pretty much simple. Ok, I'll explain.
1. Chose your .uax file which you want to open (For example skillsound4.uax).
2. Go at the C:\ directory and make a folder! (For example C:\OpenSound)
3. Now copy in that folder skillsound4.uax and l2encdec! (If you don't have l2encdec, download it!)
4. Start -> Run
5. At the Run window write down "cmd"
6. Black window will appear. Write "cd C:\OpenSound"
7. And then write "l2encdec -s skillsound4.uax"
8. There will appear new file "dec-skillsound.uax". Open it!
9. Wolaa! No errors.
10. To encrypt write down "l2endec -h dec-skillsound.uax". There will appear enc-skillsound.uax. Rename it to skillsound4.uax and you're done!
The thing is what you must know, is that almost ALL Lineage II files are encrypted. In order to take a look at them you must decrypt them. It doesn't matter what kind of format are they!