Well, the file might be was lost due to the server down 1 or 2 months ago. And, since the show is lack of popularity, maybe that is the reason why it is not hosted back. OR, the series might be removed on purpose too, such as lack of popularity, and also the RAW of this series has reached 52 episodes while the sub is only on episode 29.
Episodes that are grey are not "lost". Those are episodes that were removed from the servers because they were low on popularity in order to make room for other shows that are more in demand. Unfortunately disk space is not unlimited and FTV already hosts quite a lot of data.
Another possible reason for no longer hosting the series on the site is because fansubbers failed to continue to sub the series, thus the series was never completed and there was no actual reason to continue hosting the files for an incomplete series.