FSACC

I have somewhat of a mystery going on here. A couple of weeks ago, I used FSACC to check my roster of planes for errors and it worked fine. Yesterday I wanted to use it to change the sound cfg file for Milton Shupe's Beech d-18 and FSACC told me there was no FS2004 installed on my machine. I have not added nor changed any files except for flight plans. This is on my gaming machine that does not connect to the internet and only gets files that have been checked with three different antivirus and two spyware programs. Any clue would be greatly appreciated.