iTunes - Greek Characters problem

I have some songs in my iTunes Library that are in Greek. I had no problem until yesterday that I imported a whole album with Greek songs in my Library and its track names appeared like this: http://img30.imageshack.us/img30/8430/screenshot20090917at121.png

I searched my whole library and found out that there are other Greek songs that their track names are not shown correctly. This didn't use to happen with my Library when I was on my Windows PC.

I'm also wondering why this doesn't happen with all of my Greek songs but only with some.

Any ides that could help me solve this issue? Your thoughts and suggestions are appreciated. Thanks in advance.