It all started with custom interfaces (like Celestine or Iordanov) not working anymore nowadays, as a returning player after a long pause:). Once you replace the server files interface.u or interface.xdat in the \system folder with the interface files interface.u or interface.xdat> l2.exe it will throw file corrupt error.
The idea is to:
1. create a new folder(which will contain the interface files) inside the system folder, like system\celestine\
2. keep the server files interface.u or interface.xdat in their \system folder
3. modify l2.ini path values to load interface.u from system\celestine\
4. the post you mentioned is similar to this, not sure on the correction of typing though, the number of dots show the depth level from lineage installation folder?
a. Paths=./celestine/*.u
b. Paths=../celestine/*.u
c. Paths=.../celestine/*.u
Dont know if this works, but i gathered bits of information from here and there, since more people have this issue.