It's either the eqtext.txt or eqstr_en.txt file that is missing or corrupt. If you have those files, check them with a hex editor (not a normal text editor). The first three or four bytes before the "EQST0002" part have to be removed.
They are invisible (due to being hex < 32) in notepad, but they confuse the client
These bytes get added to the files if you changed eqtext or eqstr_en with a text editor.
Now, if you don't have those files at all, try patching.